I could not stand them. It could be that they were initially improperly installed, but when the tips came off, along with them parts of the ferrule broke off. In addition, the ferrule surface, for whatever reason was not "smooth"...almost glass like, that tended to "stick" in your hand.
Again, this might have had to do with the "installation". Some swear by them, but on the other hand I've heard of quite a few cuemakers that will not use them (I don't know their reasons).
Regards,
Doug