Hi Bruce,
I had a chance to try out the Guitar Mic at an event last week. I was playing solo fingerstyle in a room with ALL reflective surfaces. The Bartlett Guitar Mic did its job. Plenty of volume. In fact I backed off a bit so as not to blast the folks at the front.
Not a hint of feedback, and my pre-war Jumbo sounded warm and natural, just like it does when I'm in my music room at home woodshedding tunes.
Thanks for a great product,
Bruce Nemerov
http://brucenemerov.com