I have MAC's old system and its 3 years old and its been on and off probably 5 or 6 times and it only has a little rust around the welds. I also drive it through any type of weather thats thrown at me and its has held up fine. Plus it sounds amazing.
I've had one of their older systems on my car since 97 and it had minor rust until I cleaned it up and sprayed it with some hi-temp paint. Looks sounds and performs great. I can only imagine that the duracoat ones would hold up even better.
Mine has held up fine and I have the newer kit with the adjustable tips. I love the sound and theres no rust that I recall on the cat-back. Very good kit for the money, my only complaint is you have to play with the tips and the pipes to get them looking straight without rattling. But it's not bad, just have to mess with em a bit. Worth every penny imo, and still looks great underneath.
I've had a few of their catback systems and they're all great, but their headers rust all to hell and back every time, and that's in typical Ohio weather which isn't as bad as some other places. Under the hood my headers are rusted in spots but where they come down under the car they're totally covered with surface rust. It'll be the last set of headers of any brand that i buy that aren't ceramic coated.