I don't think that I really need to provide any detailed instructions about how to use this toy since I think that it's pretty clear. I suppose that it could be used vaginally, but I think it's mainly marketed as being an anal toy and that's what I used it for.
If you're a bit of an anal beginner, like myself, then you'll definitely want to stretch your ass out a bit first before trying this toy. Otherwise, it'll be pretty hard to get it in there. Just use a lot of lube and a couple of fingers, then you should be good to go!

I would definitely use this toy to prepare before anal sex (if I was getting any). The way that the bumps increase in size the further down you go makes it excellent for gradually stretching your ass wider.

This toy meets one very important requirement for anal toys - the base is flared, so there's no way that it can get lost in your ass. Besides, the toy gets pretty wide towards the base, so I know that, personally, even if there wasn't a flared base there still wouldn't be much chance of me inserting it far enough to lose it.

The Titanmen trainer tool No. 4 is made from Sil-a-Gel; a material which I've had a bit of trouble finding information about. According to Doc Johnson, Sil-a-Gel is an "anti-bacterial compound" which this company adds to some of its products. In the case of this toy, it was added to the PVC with which the toy is made.
Although I admire this attempt to keep this toy as hygienic and long-lasting as possible, I really have to say: Sil-a-Gel stinks. Quite badly. It's a kind of sweet yet rubbery smell, one which is sickly enough to leave me with a headache after a little while. Since I received my toy over a month ago, it has been left sitting outside of its packaging, yet the smell has not diminished. I only have to hold this toy very briefly for the smell to stay on my fingers for ages.

The material is smooth and slightly squishy, and the toy feels almost hollow on the inside. The material is thick enough that the toy feels fairly firm. This toy is not at all realistic.

I really do like the shape and design of this toy. The smoothness makes it very easy to slowly slide further down on the toy and open up my ass. I love the use of the increasing bulges - instead of a kind of pyramid shape which would be constantly stretching me wider and wider, the bulges mean that I can stretch my ass in stages, as it allows for a bit of satisfying respite after passing each bulge.

I think that the size of the Titanmen trainer tool No. 4 means that it is capable of satisfying people with different levels of experience with anal play. The beauty of this toy is that, as the name suggests, it is a training tool. The first bulge is definitely suitable for beginner to intermediate anal play, and I would guess that the final bulge before the base is large enough for those who are more experienced at anal play (just guessing, because I'm definitely in the beginner-intermediate category). On my first time using this toy, I managed to get far down enough that the first two bulges were in my ass, and I have hopes of getting all the way down at some point in the future.

As I said above, I really do love the fact that the Titanmen trainer tool No. 4 has the increasing bulges. In my opinion, this feature makes the toy much more versatile and gives it a much broader potential appeal.

This toy has a rectangular-shaped base, so I'm not too sure if it would be harness compatible - the only style of harness with which I am familiar is O-ring, and it definitely wouldn't fit into any of those. At a maximum, the base measures roughly 6.7 x 4.7 cm, so if there are any harnesses which could fit a base of that size and shape then I suppose that this toy could be used with a harness. It doesn't have a suction base.

According to EF's Materials Guide, the Titanmen trainer tool No. 4 can be used with both silicone and water-based lubes. Although the inclusion of Sil-a-Gel in the PVC makes this toy anti-bacterial, you would definitely still want to wash it after use - some mild soap and water is sufficient, but I have also used some of EF's toy wipes on this toy and they worked fine.

Just to minimise on clean-up (and because I have other, more porous toys that I use anally), I use condoms on all of my anal toys. Not only does this prevent any potential allergic reactions (I have quite a few allergies), it also means that my toys last longer and are less likely to retain butt smells (although in the case of this toy, that may actually be an improvement!).