The "percentage gains" I have seen posted here are worthless, and more likely to be misleading than informative. Even with a dyno, there would be errors in the estimated gains that would have to be reported.
Videos might be fun to look at, but aren't any more informative. There was a thread awhile back where people were actually voting on which of 2 saws, in different wood, in different parts of the country, at different times of year, was the most powerful.
Anyone who thinks "percent gains" or videos makes their gamble safer is fooling themselves. Great entertainment and good for barroom bets, but that's about it.
I like Simon's style. "Buy it or don't" tells me he knows that videos or botched attempts at math aren't worth the time it takes to generate them. If I was the kind of person who'd pay money to have the work done (instead of being the type of guy with a basement full of unfinished projects), I'd send him one today and see for myself.
Of course, if you'd rather hunt for someone who is willing to blow a little smoke up your ass, I'm guessing you won't have far to look.
THAT would be useful information.