My guitar is setup with one volume, a 5 way pickup selector, and a 5 way sustainer mode selector. I do wish you could have the neck pickup and sustainer on together. System was too complicated to switch out of the old guitar, didn't want to take a chance on losing it, but didn't want to switch guitars whenever I wanted to use sustain or harmonics. Good replacement for original neck pickup, but can be dialed hotter. The Sustainer doesn't need an amp to work.
Pickup sounds good though.
You can't tell the neck pickup was switched out. For Slow blues, it's fantastic. I definitely want to keep a Sustainiac in my collection. I've been playing 35 yrs. Didn't like the limitations of the old Sustainiac guitar, like using 2 batteries, having to have humbucker bridge pickup only, etc., and not being able to put it in whatever guitar I wanted.