Catch Can Questions

I know the basis of putting one in and after spending the complete day getting my intake valves nice and clean again, I am considering putting a catch can in. I have looked on ebay ( only for reference !! ) and they seem to be around £200 - £300 !!!
What benifits do they do and who or where is the best place to get one for my TFSI ?
Thank you :)

Anyone know or have done this ?

made one out of a coke bottle once on a mates mk1 golf. worked a treat.

There seems to be some sort of adapter plate that replaces the pcv on the engine but they all seem to be in the US