The flapper is nice, and it smooths out the dip in power that is seen when the flapper actuates, but I have not seen any proof that the PAIR mod does anything to help the bike, other than it cuts down on backfiring.
People claim the pipes are cooler and that there is "better exhaust scavenging", but those 2 statements are contradictory. Hot exhaust gases flow faster due to the expanded nature of the molecules. If exhaust gas goes from a hot environment (the combustion chamber) to a hotter environment (the pipe), the gas will expand and flow. If the pipe is cooler, the gas will condense and tend to pack up.
So, if the pipe runs cooler, then the plus for PAIR is a cooler running bike with less power. If the pipe runs hotter, then the plus for PAIR is just more power through better scavenging.
Which is it? SubSailor? If anybody knows, you do.