Alex, like you I have an interest in RNLI SIBs as you know, I've got a few links I can post on these if you like?
They do look interesting but for me they seem to fall halfway between a regular air floor sib and the Y Class, the keel looks pretty flat too and I reckon an Aerotec with a few mods makes a better case for a lightweight performance SIB. That's putting aside the obvious attraction of a 'service' boat.