I think the best way to use the Jack Master is to just substitute it for your hand. Pretty Simple.
I've used this toy sitting up, lying down, and free styling standing up. I prefer to use it on my back in bed, all in all.

It can be a bit of a weight, but as long as you have a good grip on it (both hands), you're not going to smack yourself too hard with it

When it comes to stimulation, it's a straight forward shaft-pleaser. One of the good parts about the Jack Master is that depth is really not too much of an issue. True, it can only hold so much; however what will fit in will feel great.

If you're on the underside of average, you'll just have more room for moving around in there.
This toy can be used pretty much anywhere you'd pleasure yourself anyway

The inner material is TPR. It feels like a mix between silicone and a jelly toy, and definitely adds to the whole package. It's both smooth and firm but with plenty of give. The texture of the material is good for simulation of the real thing. Beginners will like it because it just feels great. Advanced users can appreciate this if they've ever tried a sleeve that was too short or too tight. The outer material is just regular hard plastic casing. I also couldn't help that the smell of the toy reminded me the Transformers toys I used to get a kid.

The inside design is great. Either side has its own set of textures. One side has ridges and contour lines. The other side has a lot of nubs and stubs for added stimulation. The outside could use a little work though. It does have a habit of popping open. The designers needed to account more for the displacement caused by a fully erect penis in the TPR. The over-lapping latches also don't resist much pressure either. A better idea would've been some sort of twist lock to secure the two pieces together. The grips on the toy are great though! You can simulate a partner that is really tight to a partner with a bit more flexibility.

The toy itself can seem a little bulky. But, given what's supposed to go in it and how it's supposed to hold up, it makes sense. A handy design addition is the bottom plate. It's just a small dish that goes over the opening at the bottom. Not only does it keep the toy closed, it also prevents other things from getting stuck inside and tearing the soft bits up. I guess it could also be used as a collection dish too.

It looks and feels as though the designers of this product had the average guy in mind when they designed it. It's not too snug of a fit and it doesn't give too much room either. Given the design, it seems as though it could be used with any size penis.

The toy isn't really that easy to hide. However, the designers also made this product to resemble an accessory to pretty much any action figure collection. So you could put it with your GI Joe or Ninja Turtles on display and no one would be the wiser. In other words, it's not easy to hide but it doesn't look like a traditional sex toy either.

There isn't really much to the mechanics of this toy; you manually adjust the tightness of the inner chamber by squeezing the outsides. Because there is not set left or right to this toy, you can adjust your grip to your liking. You can use one hand to grip the top and bottom or you can use a hand on either side. I prefer the two hands approach, but that's just me.

I also want to mention the tendency for popping open. If you use both hands at the same time on this toy, you can keep it closed that way. Given the way this product feels while using it, it's a small inconvenience really.

I did use this toy under water once with pretty good results. TPR seems to hold temperatures pretty well.

Care and Cleaning: EASY!

A few squirts of cleaner/soap, rub it around into the nooks and crannies, rinse, you're set. DO NOT try to push the TPR out too much while cleaning. There are guards inside to keep the TPR in place inside the harder plastic exterior. If you push too hard, you can push the TPR right out and have to slide it back in. Too far and I don't know how you'd get it back in alignment.

After washing it, I just left it open on a towel to air dry. You could rub it out with a small cloth, but air drying seems more sanitary to me. Once it's dry, put the cap on the bottom and store. EASY! It seems to take a little longer than over night to dry. But this really depends on where you dry it.

I used this with both silicone and water based lubes. I enjoyed the toy most with both at the same time due to TPR's own feel. TPR doesn't, to my knowledge, react with silicone lube.

The package of this really screams "SEX TOY SEX TOY". So, it serves its purpose, but you can't really re-use or store it for use later. As with other masturbators, it claims "better than the real thing". Eh...dunno about that.

Other than the popping open issue that is readily fixed/adjusted, this thing is PHENOMENAL! As an extra bit of flair, I used this with the mantoy WOW. After getting used to this toy, it's very easy to use with other products in other areas.

My girlfriend got a kick out of this toy because she could see through the toy into the insides, like the window on a washing machine or at a car wash. She also enjoyed not having hand cramps at the end too.