I've heard that bluetooth latency is an issue.
There are people in the MOD forum asking about bluetooth audio connection and the answers have been bluetooth latency...
As for a potable speaker...
Fluid Audio makes a small speaker for guitar. Not sure how low it would go... but it's very portable. I saw it at their booth at NAMM and remember sounding pretty good for guitar.
http://www.fluidaudio.net/products/strum-buddy-electric-guitar-monitoramplifier