The one thing that I disliked about the mugen was the SLOP in the arms after a couple runs. The upper arms would slide back and forth and the rear arms, would move too. After running my NT1, (2 club races (30min main), 2 events(45min and a 30min) and all the qualifiers and practice..over 2 gallons of running), I still have NO SLOP in the arms. I even cartwheeled my car at the 301 race this past weekend, coming out of the sweeper at full throttle, bounced it all the way to the back straight, and the car had no damage. The plasics are excellent. I had issues with stripping screw holes out on the Mugen, but with the Xray, even using an electric screw driver, I hadn't stripped one hole yet.