Steve, I have actually installed the dual model on two 400s and two 650s they work fine. But, they do take "some" tinkering to fit and work.
The tab on the throttle lock fits between the cables under the cable retainer plate screw. This will produce a gap between the retainer plate and the metal cable holder. I made a spacer out of a modified flat hard rubber faucet washer to fill the gap. The throttle lock tab will need to be trimed in width and thickness. Also a note on trimming the plastic flanges on the handlebar throttle. You need to keep the as around a posssible to avoid flat spots.
If you decide to install one and would like to call me, my number is 423-461-3535 at home.
You also ask Paul on another topic about using the Throttlemeiser. Your description of how to use one is basically correct from my experience. I had one on a bike and never got used to using it. However, some people use them and really like them.