I have used it for the last two years - recommended by an Impreza owner who is heavily involved with it in sprint racing. Expensive, but as our WRX is involved mainly in short trips, it seemed like a good idea. At 37,000 miles, it runs perfectly and probably all in the mind, it appears to be quicker and quieter. Also have Millers Nano oils in the gearbox and diffs. Like you Graham, very fast road use where safe and possible! We love our seven year old WRX PPP and as we all know, it's no longer worth much and hence my reason for giving the old girl the best... I did refer to Millers before using their Nano tech oils and they confirmed ideal for an Impreza Turbo.