My advice for getting a PowerLock is to look for ones with 1/4" hex screws instead of ones with allen-head screws Those are the earlier ones that are built to a much higher standard than the newer PowerLock/PowerAssits lines. The older ones had great lockup and better overall build-quality.
Though, that said, I still think the newer PowerLock and PowerAssist are good tools. And as far as the PowerLock is concerned, I would get the lock tab over the piano locks, as the piano locks are cumbersome and fiddly to use. The play in the tool lockup usually isn't dangerous, and normally doesn't impede usage, unless that kind of thing drives you mad.