I have not heard great things about HMF quality. Other sites I go to some members have had issues with end cap blow-outs, discoloring (on anodized), and the need to frequently repack....maybe more than other brands. And I have heard that they can be loud, but like most manufacturers they probably offer quiet inserts. However, I am sure that given any group of people who buy a product, you will get as many different opinions as there are people.
I have heard good things about Big Gun exhausts. Everyone I talk to that has one loves them.
If you are looking for a group buy, I'm sure you'll get activity if the price is right; people love a bargain.