I had the D812 and driven it for about a year at the revelation track, this was a good kit for me as i was still learning how to control the car through the jumps and track. I then switched to MP9 and i quickly fell in love with it on how smooth and easy it performs at the track. I havent driven the D815 yet, but between the d812 and Mp9 IMO the MP9 is the best kit for me so far!