I have Sperzels on my Carvin, and (I think) Schallers on my Music Man. No question locking tuners are a huge convenience to use. I find the Sperzels to feel like the highest quality, and the Schallers feel a bit "cheaper" by comprison, but I don't mean to say they're inferior quality, just that the Sperzels seem so well made, and are a joy to use.
Brian