Before I put the 9" in the back of the Jeep, I had a 'Super 35' kit and 33's... The detroit broke once, but that was in a parking lot and was blamed on a bad cast from Detroit. I had another one read labelled to me and it was replaced within a few days. Labor wasn't an issue, since it was all done in house.
But my overall impression of the kit sucked. All right, not that bad... City driving was ok, the cheirping and banging did take some getting used to, but it was drivable. I had to pull a small utility trailer with it... The bang coming out of the rear scared me to death. I thought I broke it again.
My worst scenario was on an early morning outting, where it snowed here in Western Washington. I thought I had this bad a$$ Jeep with 33's and all these add-on's... Well the moment I got on the freeway I was freaking out. My rear-end was all over the place. I was scared to go over 30 mph. I was holding on to the steering wheel firmly with two hands, and praying that no-one was in the lanes on either side of me. What really got me was when this Ford Taurus zoomed by me at normal highway speeds. Back to this thought in my head that I had a awesome Jeep, but this Taurus certainly performed better.
Since then, the 9" upgrade, and the ARB air locker were the greatest (well another one of the greatest) upgrades I did to the Jeep.