I've just recently got a Dive-Rite TransPac II, with the Rec Wing. Without the crotch strap, I found that it was sloppy and the tank wanted to move all over the place. With the shoulder-straps adjusted properly and the cumberbund tightened a lot more than it was, plus the addition of the crotch strap, I've found that it's very stable, very easy to use, and I have a lot more freedom of motion than with my Cressi jacket-style BC. (Which I also love, by the way.) I also got the weight pockets, which are very generously sized and hold a lot more than than the pocket of my integrated-weight Cressi-Sub BC.
One thing I really like about the Dive-Rite is the steel cam-strap system. Wet or dry, once those things are buckled and clamped down, that tank isn't going anywhere! With the single nylon strap of my Cressi, the tank always seems to want to slide out, even when I've wet the strap before securing the tank. It's frustrating to have to descend to the sand, kneel down, take it off, and crank down on the strap again in order to continue the dive. (Fortunately, it wasn't a wall-dive in Cozumel!)
Someone mentioned the first-stage hitting them in the back of the head with the Dive-Rite. Just tighten up the strap that goes over the tank valve, so that the BC rides a little higher on the tank. Problem solved.
I have yet to make a real dive with the Dive-Rite, but so far, the way it behaves in the pool, I'm very pleased with it and looking forward to diving it in the ocean.
P.S. Dive-Rite Express ROCKS!! Their speed and customer service are the best I've ever seen, bar none.