saw it talked about on the s1 forum, I think for most people unless you could do the welding yourself, it would be simpler to buy the ready made galved chassis via the s1 club.
the only advantage for the flat pack was a much shorter waiting period, iirc it is about 2 months for the club one but you would get the right chassis for your number with the club one.
don't think anyone had actually taken the plunge and got one.