I use this as an interface between my classical guitar pickup (a Sony ECM-44 lav mic clipped on to the edge of the soundhole - inside the guitar - treble side - pointing down toward the bridge) and a Roland Mobilecube. The results are excellent. It's an all battery powered set up. The Fishman takes a 9v and the Mobilecube takes 6AA. The Sony lav mic takes 1AA.
One of the best things about the Fishman is that it has a notch filter. Really cuts back on the "woofiness" along the bass strings. There's decent EQ (I leave it all set flat) and a brilliance slider (pumped up slightly).
I can't stand the sound of under-the-saddle pickups in classical guitars. And I don't like to set up a mic stand and external mic for gigs. For weddings, church ceremonies, etc. - any place you need battery powered amplification with a a true sound - this is the way to go. It's not terrifically loud, bear in mind. But loud enough in the right kind of situation.
I couldn't go directly to the Mobilecube with the Sony lav mic with any decent results (going into the mic input on the Mobilecube). Feedback problems, etc. This is where the Fishman really shines. It enables me to control the signal before it reaches the Mobilecube. In this way, I go from the Fishman into the line input on the Mobilecube. Much louder and purer sound.
All you classical guitarists out there who gig, take note! You need this DI!