I put this in my cr250 years ago and felt a bit better pull.
I put the now and plus in my CR450R and did not notice much, slight better pull. On the dyno there is not power gain. I had my engine dyno pre and post and their is nothing. The ads of 1hp claim is truely not true! When I spoke to Boysen the even admitted to less than a 1/4hp and said the plus insert adds nothing. For the money spent you are better off adding a CAM where you can feel and dyno real power. Also you do lose the ability to adjust the air screw on 4 strokes - thats right! you must leave the air screw open to 2 turns out, if you do not, the bike will have hard starting! That is a fact that is writen in the documentatin from the vendor.
When i purchase a new bike next year I will have the engine done with a cam and not spend money on this device. For those reviews claiming tons of power, I ask did you have it dyno? Every engine builder will tell you you will not see anything on a dyno, but I will say it does seem to provide a slight pull ability from gear to gear.