because dedicated tools usually work better. if you're going to put serious hours into wrenching, get the better, dedicated tool. if you're just a home mechanic that will only need a lockring wrench every few months, get the shimano.

and if for some reason you need a lockring wrench and chainwhip on the side of the road (because your home mechanic skills get you into constant trouble when you finally take your bike out), get the trixie tool.