They are great for time trials and short stints, but when you can kill them in a weekend aren't ideal for the typical track dayer like me.
I plan to stay in the true 200tw category for a while. Or as long as they continue to make them.
I might be a bit biased since I just started running them, but the RC-1 is a terrific track day tire. I'm using them for TT where they're not quite grippy enough for the job, but I love this tire already. Well behaved, drives like a 200TW street tire without the tread squirm, lots of audible feedback, and should maintain the same grip all the way to the cords unless you're camber limited and murder the shoulders. If you don't have the ability to bring an extra set of wheels/tire they obviously don't work out, but I'd choose them over any street tire any day...except a rainy one.