I had one some time ago. I don't hear a huge difference from one soundboard transducer to the next. I think placement and the preamp you're using have more to do with the end resulting sound than the bug(s) itself. FWIW, I've ended up with an earlier generation McIntyre in all my guitars and my daughter's harp and a JJB in my uke.
I played around with one briefly, but not long enough to form any real opinion (and it was an unusual project). I'd suggest calling the guys at Shorline Music - John has worked with their pickups extensively.
I have a buddy who used one for a while on his flamenco guitar. He thought it sounded better than an under-saddle piezo, but was dependent on experimentation for placement, and that handling noise was annoying.