This little device does away with felts or anything else you put around through your cymbals to mount them. Its a small round piece of plastic/rubber that goes through the hole in your cymbals and then slide it over the cymbal mount on your drumset/kit. It stays with the cymbal and will NOT fall out. Saving you setup and tear down time, and your pocket because you don't have to buy sleeves, felts or washers.
Its a bit tricky to get it installed but once you've done the rest go very quickly. And you can remove them after installation, again it just takes some patients.
I personally have used them with brass and Yamaha PCY cymbals. Because of the mounting system Roland uses they are not practical.
(not a paid Grombal spokesperson)