So, I've rehearsed with them using guitar and bass, and gigged using guitar.
I use them in the house for practice, both in to the amp, and in to the laptop - via a Line 6 GX.
The only issue, as stated earlier, is that due to the position of the transmitter on my guitars and bass, I can't see the power light to know when they are getting low.
But I just make sure they are charged before a gig, so no problem. They charge quite quick too, around 2 hours or so.
I'm loving them [size=4] [/size]