I've used one in a normal covers rock band, and found it great fun, but not massively flexible. They don't sound like a conventional bass guitar as the sound doesn't have a lot of highs or sustain, but you can get a nice mellow double bass-like sound out of them, and the close fret spacing also allows the playing of very tight, fast bass parts with very little finger strain. As the strings are rubber, you aren't going to get the clang and grind that's important for a lot of rock bass sounds, so in a really rocking setting you won't sound (or, necessarily, look) the part. In a jazz band, a coffee-shop semi-acoustic band, or something softer/quirkier, it could be great.
You do, of course, need it to be amped up to get much sound out of it at all, and I've had problems with noticeable hum from the piezo pickup - plug in, turn up, and make sure yours doesn't suffer from that problem before you commit to it.