[Kevin M]

Another effect to consider is that if the thermostat does manage to keep your coolant temps down,t he ECU will never bring the car out of coldstart mode, which means lost power and worse fuel economy, especially in city driving. I'd pass on it for a street car. Heck, I had a Crucial Racing one sitting around when I built the RS, and left it out in favor of a new OEM one, and that car sees a much higher percentage of race use than any car not also a dedicated autocross/track car. The open-fail feature is nice, but probably not worth the tradeoff unless your car spends tons of time at the track where the extra enriching on a boosted engine could be a good thing.