Whilst I can't vouch for Ikon Bodyz as I've never used them, I think it's unfair to say things like "steer clear" or "cant even spell" if you've never used them. They're busy - that surely tells a story in itself? Yes, I believe that they are more of a mods kind of place for boy racers, but that doesn't mean they don't know their stuff with bodywork in general. If people give them negative feedback based on actual experiences then that's acceptable enough, but otherwise please all think before making public assumptions. This forum is read by thousands and could affect their business when (as far as I can see at the moment) they've done nothing wrong. As for the spelling - they have a general target for business and the name is deliberately mis-spelt in order to appeal TO that customer base. Nuttin' wrong wid dat bro!
The title asks a question. "Has anyone used...?". I personally would like to hear feedback from someone that actually has. Especially if their pricing is so keen because I may consider them in future if the feedback was appropriate. I'm reasonably cheap as a computer technician compared to some - but it doesn't mean I don't give 100% to the service I give.
Whilst I can't personally vouch for either, I have heard a few myself say that Body Matters are very good. As the OP says though, there's a considerable saving possible so it's understandable to try and get some real feedback before shelling out hard earned cash.