One of my best friends works for KW suspension and tunes suspension for formula drift drivers running KW setups (mostly japanese cars), and he swears by raceland as far as quality for the price goes. I know I guy who used to run a high end brand (cant remember what it was) on his 325i but when they blew up he switched to a raceland setup and loves it. And this guy drives his car hard.
Basically he says raceland cost is low because they're starting out and need to get their name out, but they're great quality especially for the price. I've never talked to anyone who hase used them on a mustang, and I am not about to install them on my car, but i have heard good things in general.