I've used one for about six years and would like to give a big -1 to the tremelno.
The basic idea is great . . . you just do up all three thumbscrews to have a fixed bridge, or one thumbscrew to have a dive only bridge. In practice it doesn't work as it's supposed to:
The unit works by adding some blocks that fit over a smooth precision rod, one end is permenantly attached to the claw and one end to your trem block:
There is only one little screw to hold the trem in place for dive only . . . and I found that under regular use this screw wasn't enough to keep the stopper from slipping a little after use. If you broke a string or something, the stopper wouldn't work at all. If you want to increase the spring tension enough to do double string bends in tune, the single screw won't hold position properly. You can try tightening the screw even more, but it just won't hold very well.
All three screws tightened do not hold very well either. Certainly not enough to do a string change, maybe enough to prevent slippage from a string break depending on the string. There is enough to do two string country style bends occasionally.
"Why not crank down hard on the slipping screws?" You ask. Well, that's what I eventually did. Cranking down hard on the thumb screws makes gouges in the smooth rod . . . and these gouges mean that your trem will never return to tune properly because of the added friction in the system now. Yes, you could probably pull the whole thing apart and then sand the rod back down to try to make . . . but I eventually just said **** it and took it out.
YMMV and all. I use 11 - 52s, so maybe if you use 8s it would work better?