I haven't tried one but it should work fine for a practice amp. However it wasnt until I strayed on to this picture that I realizes how small it is. Those are AA batteries as far as I can tell.
The Delay knob and the line-in port are nice features. It means that you can jam along to backing tracks and karaoke files.
I myself use a small karaoke machine for practice. However this is 120 volt and would not be as portable if your purpose was busking.