Really hard and strong picks, probably not suited for acoustic playing...
I bought them just for the fun of it, along with their "twins" Harley Benton PB1 Bone Picks, mostly out of curiosity, and tried them out on my acoustic guitar so far.
These particular ones are pretty beautiful and although a bit slippery, they have nice overall handling.
They produce a pretty strong and "plucky" sound on the strings, nice for experimenting a little bit but they are probably more suitable for basses and stronger strings in general!
You should try them out, however, no matter what instrument you are thinking of using them on!