Yep thats an excellent price, magnaflows usually retail for around $300 depending on the model. Some exhaust shops I have spoken to said that the magnaglow can be a bit 'boomy', but then they were trying to sell me a muffler that cost twice as much. They are a quality muffler so go for it!
Yeah I was looking at getting a Remus muffler and then could'nt believe the price, magnaflows are supposed to be a very free flowing muffler, so i guess if it flows better than the stock item you would see a small power increase but i don't think it would be much.