Re: Locking tuners...
I've tried sperzels, schallers, and grovers.
Sperzels are probably my favorite, they feel real smooth, have a nice modern look to em, and the string lock mechanism feels real solid.
Schallers are cool tuners too, though on some of my axes the lock mechanism can get stuck before it tightens all the way, not a huge problem, but enough to be irritating. They're real smooth in tuning though, probably even better than the sperzels.
The grovers honestly I don't care for too much. It just seems to me like the posts are far too tall, at least taller than the standard non-locking grovers. it somewhat defeats the purpose of a tilt-back headstock, and i can imagine it might cause some problems on a strat-style headstock. The unwound strings tend to slip a little bit in them as well, though that mostly only happens when you first start to tune up. However, it has happened to me occasionally while i've been playing.
Positives though, they're real smooth, great feeling tuners, and if you've already got grovers ya dont have to drill for new tuners.
I almost installed a set of planet waves locking tuners in one of my guitars, but had to return them cause I needed a 6-in-line and they gave me a 3X3. One thing I noticed on the negative is that the lock mechanism comes out of the tuner when you unscrew it. Not so much of a problem if you're careful, but if you lose it you're f***ed.
my .02
*edit*: Though, after looking at the ad on the stew mac website, it seems their grovers have somewhat shorter shafts than mine. maybe a new design? I dunno.