I have so many watches that paying a jeweler to swap out the batteries was getting just too expensive. I bought a few tools to pry open the snap open/closed cases but the twist off backs were another story. I bought this to solve the problem and have used it successfully to open some super tight dive watch cases and - being extra careful - I didn't scratch the backs.

It's not a precision tool - the gear mechanism is a little sloppy. You need to know which direction to spin the knurled wheel to loosen or tighten the grippers. And as has been mentioned by others, the grippers are made of a tough steel and if you slip, you'll score, scratch or gouge your watch's soft metal back. Use caution!

This tool has already paid for itself and at the extremely low price, it's kind of a no-brainer if you have a few screw-back watches.