need a cat/decat making up as the fitment to the exhaust is different. 182 exhaust wont fit a 172 without cutting the spare wheel well out and fabrication a new boot floor and mounts
Benefits are all midrange. Plenty of discussion about this on here recently
I believe you can buy a 182 style exhaust though that fits with a wheel well
Buy a manifold, new gaskets and a link pipe. Job done.
Great upgrade IMO.