I'll first say that I've been using Schallers pretty much from the start and I'm extremely happy with their performance, except when using them on a guitar where the front strap button is in the heel of the neck (ex: arch-tops, acoustics, SG's, ESP Vipers, etc).  When used on these types of guitars, the "unlocking stem" of a Schaller can poke you in the stomach and be very uncomfortable.  For this reason, I decided to experiment with the Jim Dunlop design.