Maximum motorsports here. Great quality, I highly recommend. But yeah, they're not the cheapest around. Are you more into straight-line performance or corner-carving? I chose the MM arms for the latter reason. Control arms with poly bushings are not the best choice for corner-carvers (excess binding) but work great for drag racing or normal daily driving.
I had UPRs on an old car and they were garbage. I had double adjustable uppers and they WOULD NOT stay at the length that I'd set them at, causing my rear end to get crooked and causing major tire rub and it wouldn't drive straight at all. Not to mention they were noisy! noisy! noisy!! Everyone else seems to love UPRs crap. I think their stuff is just that. Crap. I switched them out for ones from UMI Performance and they were great. MUCH more quiet, better ride, no stupid problems. I'd recommend Maximum Motorsports or UMI. I hear good things about some of Steedas control arms, too.
In my experience on my car, the control arms I got didn't do diddly squat for me at the track. I bought the D&D econo box. 60ft times stayed the exact same.
Go with steeda. Steeda works with ford to engineer parts for the mustang. They offer a wide variety of setups also you can get stuff for corner carving or you can set your car up for drag racing or in the middle of the road. And from my experiance with them they have great customer service, the guy that has helped me every time talked to me for an hour one day about my car and what rout i should go for what i want it to do. And i am very pleased with his choice. They are a little expensive but you get what you pay for
i really like my mm rear lca's--i still have stock uppers and they will stay that way(i also run a phb though). i stepped up from some decent lca's with 2 piece poly bushings--the mm have 3 pc. i can say that i really notice a difference when coming hard out of a corner. the car is much more stable and does not want to go too far sideways.
imo mm makes some of the best quality parts in the mustang aftermarket.
I've had them for a few months now and they've been just what my car needed. Daily driving is much better than the worn out stock stuff. Handling/cornering is now loads of fun. My confidence has gone up big time.
On a side note, my stock stuff was so noisy. The new MM arms and FRPP uppers got rid of all the little noises in the rear.