The MK5 GTi engine is not suited to an atmosphere (woooossshhhyy) type valve, I spoke to Bruce at Bailey motor sport a few weeks ago on behalf of a customer. he informs me it a complicated development project they might look at in the future.
What a complete load of poo that is!
Forge Motorsports released a full Atmospheric BOV for the 2.0 TFSI Engine over 18months ago.
It's only complicated if you don't have a donor car to play with and understand how the VAG/Bosch ME9 ECU works.
If you really want one, here's the Forge product.
http://www.forgemotorsport.co.uk/content.asp?inc=product&cat=1703&product=FMDVFSiTIt does work no problems. Friend had it for a while, but has since sold it. His reason...bit too chavvy for a Golf GTI.
Great on an Evo or Scooby doo, but in a grown up hot hatch like a GTI...nah.