from a retrofit/modification perspective this sure is a great resolution to the problem of getting perfectly aligned ferrules when drilling on a completed body. the block also features a lip to cover the sharp finish edge on a retrofit installation
I'll be investigating these on an upcoming build that has individual string ferrules. For this investigation I'll complete the bass as planned and visit a studio to record a couple lines, return back to the shop and install a tone bar, and then revisit the studio to re-record the same lines. I should be able to post up sound clips to satisfy your listening curiosity about six weeks from now
all the best,
R