I have a Dynojet kit and full Yosh exhaust. Power is great; 2nd gear moonshots if I try and the frontend dances in 3rd. The mileage sucks! I went from about 50mpg to 40. I think it may have something to do with Dynojet instructions putting the floats at a near "flood the carbs" measurment.
Since I traded work for the kit and exhaust, no real money was out of pocket and I'm glad I didn't spend the money ;)
Were I to do it again, I'd build my own kit with shims and cut a hole in the airbox, get a new mid pipe made out of stainless tubing and either mod/gut the stock can or find a cheap slipon.