This and all other Meinl Cajon Castanet products are great and very cheap ways to add some variations to your grooves. Sound is ok, not amazing.
The sound of this castanet (jingle version) is more interesting than the regular one. It's very cool to use them together.
I also used them in my minimal set (practice set I would call it) in the bedroom as feet pedals!!!
They stick to the Cajon surface quiet well, and didn't leave any stain.