Depends. I am not sure exactly what you are asking here.

They can be pretty valuable to engines that have high crankcase pressure, they will clean your blowby. You would be supprised in how much oil some engines will spit out, and oil in your intake/turbo system is never fun. It also prevents oil from excaping onto the track if you are running a breather.

Overpriced? Probably.
Needed? Not necesarily.
Gimmick? Sorry, but they have been around a while and serve a purpose.