I installed Moose Racing thumb throttles on both the 400ex and 450R. The Motion Pro twist throttles worked fine but it was just too hard to control in turns.
After some play riding in Glamis and testing in the Arizona desert, the Moose thumb throttle is working well and is fairly easy to push. The longer lever takes some getting used to since it places the idle position a lot further back.
The thumb lever was binding against the brake lever dust boot on the 400. It needs to be a little further out on the handle bars so they don’t touch. I had to trim the gripto get the thumb throttle body where it needed to be.
The throttle stop screw on the side of the thumb throttle walked in on both units and made it impossible to give the bike any gas. Loctite fixed that.
I also had to go back to oem style throttle cables. The ones that come with the Motion Pro twist kit are too long.