I have a Capreo setup on my Birdy, and it works really well. It doesn't have quite the range of an 11-34 though, so if you need a particularly high or low gear, you may be best adjusting the chain ring size on a wide range cassette. I'm considering getting a 53/39 crankset for mine - I find it both a little low on the high end and a little high on the low end. But really, it works well for most things, I'm just nitpicking
