Only thing thatd put me off the Hill Power filter is that I dont think its sealed. If it isnt sealed, then I might as well just stick with my current K&N filter which I have located in front of the battery where the standard air feeds are.
Still, it does look mighty good and I bet it sounds nice too.
Regarding the PiperX Viper, I think Nick Hill has said he doesnt think the Vipers filter element is big enough for 172+bhp. However, those people running Vipers seem happy with them and they are sealed too...
I think the car on the web site belongs to Cliosport member ak_uk. Hes had that filter fitted for over a year, so PM him and ask (although Ive not seen him on the forum for a while).