I use these on an acoustic ubass and tried on a regular bass too. A rather soft tone somewhere between fingerstyle and pick style. Do not recommend on metal strings, it will shred the leather. Can't imagine it on electric guitar, would be like a cheese grater. Can't wait to try them with the to-be-installed Thunderbrown rubber strings on the ubass, seems like that will be it's intended use.
Definitely an interesting and fun little extra thing to throw into your basket e.g. if you're going for the delivery fee limit!