Tom, I accepted a recommendation to have an I-Beam put in my late wife's Hagstrom J-45 and even if I want to practice amplified at home it won't go loud enough without feedback and the sound is diffuse wooly and unclear. It's an active one with the stealth volume control so it wasn't cheap!

I tried B-bands and they were unreliable, and the only was to get a decent sound out of my Martin OM-1 was very careful off-board blending of the UST and AST(but one goes like the treasures in my mandolin, go figure!)

I used a Shadow powerbridge with a Fishman preamp in my daughter's Sigma and that sounds pretty good.

The Fishman in my borrowed Lamaq sounds rubbish, but the Fishman setups on the Taylors that I looked after for a while for a friend sounded good but a bit electric.

The Schaller bottletops I've tried sound awful AND feed back. The Ashworth stick-on sounds less awful but still not all that and also feeds back a lot.