Hey Mike,
I've never actually had the opportunity to have John work on my basses. I usually have my basses set up here in Boston before I head out of town. My buddy Albie has John set his basses up which run the gammut from his original Tobias, to his Fenders and Warwicks.
I've seen John's work as I'm sure you know it as well. I wouldn't have any reservations about having him work on my Alembics seeing what he's done with Albie's basses.
Peace,
Dino