The A-Bomb, crafted by Tantus, is an advanced level anal plug. I am not kidding when I say advanced, either; it's very large and requires a lot of care during use.
Its main purpose is to be inserted into the rectum through the anus and left there for some amount of time, whether during intercourse, masturbation or simply just to stay there a while. Like many plugs, it can be worn under clothing, though how conspicuous the base is depends on your own external anatomy. That is to say, if you've got small buttocks, it may show slightly.
On a side note, it could be used vaginally by the very brave and daring. I don't really recommend it as it's got quite a presence. Make sure it's been well-cleaned if previously used anally.

Moving along, though... Use of this toy, like I said, requires more warm-up, lube and caution than some smaller products. I think it would be best for anyone, even very advanced users, to first warm up with a smaller toy (or a series of smaller toys), as this will ensure that you are adequately relaxed and lubricated. Successively larger butt plugs may be a good idea. (I used the O2 Cush, as it's already fairly girthy. Even then, the A-Bomb was quite difficult to insert the first few times.)

Once you're warmed up, move on to the clean (and hopefully lint-free) A-Bomb. Make sure it is coated in thick, water-based lube that you find effective. Relax your anal sphincters and breathe deeply if you desire (but be sure to breathe in any case). I found that relaxation was aided by teasing with the tip of the A-Bomb. Once you feel ready, slowly proceed to insert it, pushing very, very gently and stopping at the smallest sign of pain or discomfort. I found it helpful to stop and remove the toy just slightly when I felt discomfort; I then felt myself relax further within a few moments and progress could then be made.

A few further tips for use:
- It sometimes helps if you rotate the A-Bomb as you're inserting it; this seems to have both a relaxing and coaxing action that eases insertion somewhat.
- Be sure to hold onto the base; once you've reached the widest point of the plug, it has a tendency to move very quickly into the rectum. While I feel the base is secure enough to resist being sucked in entirely, the quick change from huge girth to smaller width can cause pain and damage. Holding onto the base will allow you to slow down the tail end of insertion.
- When removing, you need to relax just as you did before. Grip the base but don't pull; push it out naturally by bearing down, manually encouraging only when necessary. Like before, be sure you hold onto it because it can eject very rapidly, resulting in pain and/or injury. Ease it out as slowly as possible and don't be afraid to take your time or allow it to retreat temporarily.

Phew. That last section was long, wasn't it?
I'll be brief about the material... It's Tantus' 100% premium silicone, meaning it's hypoallergenic, non-porous, odourless, tasteless, phthalates-free, body-safe and feels great. It's boilable, bleachable and dishwasher safe to boot; more on that later.

I was first a bit scared after ordering the A-Bomb. A lack of RealSize images and my impression that the material would be very rigid were both intimidating as I'd ordered the product on a whim.
Luckily, half of my fears were dispelled. The silicone, while not as soft as the supersoft in O2 products, is happily a bit compressible. Furthermore, the velvety surface made me feel a little better about the whole thing. This texture holds onto lube fairly well, which is important in reducing drag. Otherwise, the surface is matte and without any lumps or bumps. It is also completely seamless, which I've come to expect of Tantus.

Because it seems to be a prominent feature, let's start with the A-Bomb's size.
Here is a photo set of comparison images if you wish to see them. I apologize for the quality, they were taken with a webcam.

Length: 5.5", ~4.5" Insertable
Diameter: ~2.5" (Listed as 2.25")
Circumference: Just over 7.5", Neck circumference: Around 5.5"

Yes. It's big. There are bigger toys out there, for sure, but I've made the A-Bomb my absolute upper limit of girth. Its diameter is slightly larger than the listed one, being almost a quarter inch wider. I feel it is just short of being too big for me. It's a very well-designed toy, and it feels great, but I feel I am pushing my limits almost too much with it.

Moving along to the design; I really like it. Unlike "traditional" butt plugs with a narrow tip and the widest point just before the neck, it has a curved, semi-ovular design. It is a little like the Ryder in that it is a torpedo-style anal plug.

The base is super comfortable and fits nicely between the buttocks while preventing the toy from being lost inside the rectum. It is flexible and can be bent completely, but I haven't had any problems with it being too flimsy to keep the toy safely outside of my body. I also enjoyed that, once it's inside, it provides a very full sensation and lots of internal stimulation; its shape contributes to hands-free use with sphincter muscle contractions.

Tantus has its logo stamped on one side of the base; unlike older Tantus toys that exhibit a hand-etched "TANTUS" and the year it was designed, this one is the official logo. I thought it was a nice addition, and it doesn't interfere with play at all.

This toy isn't realistic, but I wouldn't call it discreet as it doesn't look like an object one would use for "normal", everyday tasks. I wouldn't leave it out on the coffee table. As for travel, it has no metal or mechanical parts, so it should be fine... Just keep it somewhere out of sight.

Big and challenging, the A-Bomb delivers sensations as drastic as its size.
Again, I love the shape of this toy; it makes for very nice sensations while inside, and the size provides excellent fullness. The feeling of stretch that it gives is unreal, and the neck is still pretty wide at 1.5" diameter, so it's very satisfying.

Despite its large size, it can be worn comfortably for some time. While I would never, ever wear this for as long as my Njoy Pure Plug Large, I have worn this for upwards of an hour (under clothing) before I had to remove it. It's not great for extended wear in my mind because of the large base and massive presence.

The base is very comfortable, and the toy stays in place admirably. I mentioned hands-free use with clenching of the anal sphincter muscles; doing so, followed by bearing down, allows the user to pull in and push out the toy a good inch or more. It feels fantastic, stretching the sphincters on the way out.

I would like to add that its sheer mass did provide some noticeable prostate stimulation for me. While it is not targeted, it is definitely there.

The A Bomb is made of 100% silicone, making it a breeze to clean. I always use warm soap and water, and it seems to be just fine. While I have found that silicone anal plugs do occasionally hold onto odour, this does go away if you let it air out after cleaning it. I've also used a nice natural shampoo, lathering the toy and letting it sit a while; this has also worked.

Be sure what you're cleaning it with is free of silicones because they can damage the toy. If silicone is in the soap, it won't necessarily be listed as "silicone"; "-methicone", "-siloxane" and "-methiconol" are some suffixes to look out for.
Because silicone lubes also damage silicone toys, be wary of using them. Tantus toys are very high quality silicone and may resist any damage from quality silicone lubes... But always do a spot test on the bottom of the toy's base if you really must use them. Otherwise, use water-based lubes. Oil also works, but I generally don't like them for their difficulty of cleaning and potential risks of using internally.

Storage of the A-Bomb is pretty simple; while the box it comes in isn't ideal storage, the A-Bomb isn't picky about where you put it. Store it away from sharp objects such as knives and cats, and away from silicone lubes and low-quality material toys, and it'll be happy. I keep mine in a lined wicker box with the rest of my metal and silicone collection, but any number of storage ideas will work.

The A-Bomb comes in typical Tantus packaging. While it is always tasteful, and completely recyclable, it lacks discreetness due to its clarity. It would make an excellent store shelf display, however, and is fine for gift-giving since it is free of naked people pictures and other obscenities. There are a few colourful parts of the package as usual, the Tantus logo and some information about the company, but nothing about use (which is usual for sex toys, as they are sold as "novelties").

A-Bomb is a beautiful but very big toy. Please know what you are getting into (or what will be getting into you) if you plan to purchase this toy. It really is for advanced users only. I don't really consider myself advanced, as such, and it took me a few tries before I had any success with the A-Bomb.

It's an excellent plug, though. A safe material, an inspired design and plenty of fun to be had for those who are prepared and capable of taking it in.

For me, the third time was a charm with the A-Bomb. I don't usually like giving too many details... It feels kind of graphic. Be warned, though, as I will be telling more this time around:

The first time I tried it, I was lying on my back. I could only get it in about halfway to the largest point, and even then it was a bit of a stretch. Turning it as I pushed did help me get almost three-quarters to the largest point, but to no avail.

The second time, several days later, I tried sitting on it, though very gently. It got a little further in, though I had to give up after about thirty minutes. Despite not getting it in, there was a lot of natural lubrication going on, if you know what I mean.

Trial number three, a few days after the second, was a success, though an overwhelming one. Trying the sitting method once more and failing, I decided to return to the back-lying position, twisting it in. It stretched me, bit by bit, and when I thought I would have to give up again, I gave one more slight push and... It was as if time stopped for a brief moment. It settled into place as if on its own, and I felt this overwhelming sensation that I won't be forgetting anytime soon. It was in. I couldn't believe it. I was shaking. It was amazing, although the fullness was almost uncomfortable because I wasn't accustomed to it.

Since then, I've gotten it in each time, and it seems to get easier with each successive attempt. I really do love this toy, though it took some time to conquer it (or be conquered by it, it seems). It really is well-made, and provides the most intense feelings I've ever had, anally speaking.