Do you mean the optional 36K mile warranty? They mention it on their website but there are no details on it, which is really helpful. My gut feeling is that it'll come with a lot of get out clauses, hence the reason it's only offered on the stage 2 kit.
Regardless, any FI addition to an engine IS going to harm it. You can do it as properly as you like, but unless you're going to build an engine for it then you are going to get increased wear and tear across the board. You could halve the life of the engine easily. Would it bother me? Not a jot. My own MR2 has an aftermarket turbo conversion, and I'm fully aware of the risks of it going pop, but I'm also not letting it bother me.
What I will say is that I would never buy direct from the US on something like this, as it's a lot of hassle if anything goes wrong (been there, done that, nearly bought a plane ticket to go and sort it out!). Pay a little extra and buy from a UK supplier, that way you've got all the law over here to fall back on which is much simpler than faffing around with different laws from different states.