Honestly? I'd say save your 40 bucks. With your hand, you can grip completely around your penis (if you want), or at varying degrees of "encirclement." With that thing, you're actually making contact with only a small portion of the penis at any given time. Out of 360 degrees around, you're probably not contacting more than 150-200 degrees or so.
They offer some good suggestions (for free), like hot water warmup, slow (4 sec.) reps, etc. Follow that, if you want, but use your hands, not some bizarre salad tongs with rollers on them.
And, to answer to your sig, "Yes, 'this shit works'." It's very individualized, so there is a learning curve. It could take you awhile to "get it right." But stay consistent & you'll see gains - & become a "believer," I know I did.
Save your money, it is nothing more than a canning tool found in meijers or any store that carries canning supplies. It retails for about $4.95. You can find larger rollers at any hardware store . I still wouldn't waste your money. You can duplicate it for under $8.00. Personally I find using my hand is better and more effective. Hope this doesn't step on any toes...