STH,
I use them (sperzels) on my f@#$ed-up strat and they're really pretty cool. Very easy to string-up, just pull the string straight through and crank down the lock...great if you break a string mid-set and need a quick change. They seem to have about the same mass as regular tuners so they don't seem to affect the sound. The key, though, is a properly cut and smoothed nut. If this isn't done right the strings will get hung up and come back sharp every time you wang the bar. I haven't been into the bar that much lately, but when I was I could make those strings look like telephone wires and they would come back fine. (graph tech nut helps too).
peace.