I've often thought about an ABG (acoustic bass guitar), to have something to just grab without plugging anything up when the notion strikes me.
Since I only play fives, it's somewhat pointless, inasmuch as it's a lot to get anything approaching bass tone out of a jumbo guitar body with four strings, much less trying to coax low C's and D's out of one. Oh well . . . .
I've tried several in only the most casual manner and haven't yet found anything affordable that hit me. I tell myself I'll grab a Michael Kelly on EBay cheap sometime, but haven't gotten around to it yet.
Here in Nashville, I did try a Ribbecke Hafling that wandered through Geore Gruhn's, and I must admit it was fabulous: It also cost as much as a used Alembic, so it was a non-starter. If you can afford that amount of $$$, I can heartily recommend it, a LOT of amazing design going on in that box.
I would definitely recommend the same warning that applies to most lesser piezo-equipped guitars: The output generally overwhelms most conventional guitar and bass amps, so you really need a baby mixer or something like this terrific BOSS acoustic processor
http://www.bossus.com/gear/productdetails.php?ProductId=570&ParentId=259 . . . . in line between you and an amp, to settle down the high output (in some cases 3 or 4 volts (!) and very high impedance. That's how cheap or older piezo guitars can sound clavinet-like. Newer and better guitars are buffered, but you need to know if the guitar in question is one or the other.
The TI ABG strings are also very interesting. Turner realized that piezo bridges have no real need for a ferrous core as it's vibration that creates the tiny voltages. So they have a nylon core with metal wraps, a concept he worked with TI to create, and these are the OEM strings on Renaissance basses. Of course they work on any piezo ABG.
And, a LOT of guys use the Rob Allens in studios and roadwork out of Nashville, very well regarded.
J o e y