the PF system works, I installed one on my 172 a few years back and the results were instant, with the aircraft held on the brakes the engine produced 100rpm more than for identical conditions prior to installation, I have no idea what the climb improvement was but at max weight we get at least 200fpm more than the book figure and about a gallon an hour reduced fuel burn in the cruise to boot.
Yes it weighs more but only a few kilos more than the stock exhaust, but this is the only downside as far as I can see.
and no I don't work for them.