I bought a 2-1 for a CM400A 2 years ago. I got the painted head pipe and chrome can. The paint came off the head pipe after the first ride. MAC did not follow through with an RMA as promised, and I got tire of bothering them. Eventually sold the bike.
The pipe was loud and buzzy. I had to stuff fiberglass inside the can to get it reasonably quiet. It was not a "performance" sound, just annoying. The bends on the head pipe were not accurate, I had a lot of trouble getting it lined up straight. I replaced the mounting hardware with stainless steel because the cheap screws, bolts and nuts they sent would have rusted in a short time.
The pipe was made in China (the nice girl on the phone admitted they only coat and packaged it in the US) and for what it cost them to make and then charge over 200 dollars for it they should use better coatings, decent hardware and QA it better.
Performance? Didn't notice a change. They claimed no rejet required, I think it ran a little lean until I stuffed the can with fiberglass.
The baffle in mine rattled like a paint can. I had to wrap the forward section with muffler tape and tap it back in to keep it from rattling at certain speeds.
I'm no fan of MAC pipes, I'm sorry to say there are few choices out there. Next bike project I see with bad pipes I'm looking at what is available besides MAC, including OEM on ebay.
Of course there are probably plenty of satisfied customers who love their MAC pipes. I've never met anything but disgruntled customers who said "they were the only thing I could find".