I think it sounds fine for what I use it for, which is guitar, but it seems impossible to get anything but a distorted signal from it, which could be less useful for keyboards. I think the Banshee is really designed for guitars.I agree. Parts express has some decent horn drivers for around $30. A friend of mine had a banshee (the one with the built in amp) - it sounded terrible.
I think it sounds fine for what I use it for, which is guitar, but it seems impossible to get anything but a distorted signal from it, which could be less useful for keyboards. I think the Banshee is really designed for guitars.