Graeme,
Have fitted 4 of these so far, the only difference i can see is the tubing is a little bit more solid i suppose is the word to use, the existing is a little flimsy!?, It is still perforated !
It it were me i would order the std RAI & then go from there.
If you decide to change your mind i can run one up to you....:p:p
Cheers
