I love mine... I put it on a couple of months ago, and notice the difference daily, but really notice it when I'm towing which is why I got it in the first place.
I have a 21ft trailer that is around 4,900lbs loaded up with all our stuff, and it sagged pretty good before. Still drops the rear end, but not outside of what I would consider normal.
I have the 7-pin harness on mine, so I just drilled a hole in that bracket and was able to get my air valve there, so it is accessible without having to go under the car at all. Makes it easier to add/release air before and after every trip.