I had the Bayson R fiberglass ones, install was a pain and the fit was only OK. Got into a small accident and one side was totally wrecked (since it's fiberglass).
Just received the new set I ordered from Best Racing Motors, they are indeed urethane. Will be installing them next week so I will let you guys know how it goes. Since they are flexy due to them being urethane, in addition to using the stock mounting holes it looks like you are supposed to screw them into the OEM STi skirts, which I'm not thrilled about. So we'll see what happens