I have the Ground Control 3 on a 2013 Montana High Country. I had HORRENDOUS problems with the level system for the first year. Went through three sets of front legs because the elevating screw kept stripping. This would happen when one leg would bind up, this caused the leveling system to sense a current overload in that leg and shut down (just that leg), but the other leg kept elevating until it stripped. Could have been a circuit board problem, that was replaced with the last set of legs. I've had the current set of legs on for about 6 months now with no problems. Hopefully, it was just a couple set of bad legs and it will work OK now. I have checked around and have not heard of others having the same problems I did.
That said - having a leveling system is great. It saves a huge amount of time and effort. Also, the floor is a lot more solid compared to the old manual stabilizers in the back. I wouldn't let my experience discourage you from getting the camper with the GC 3.0 system.
Don't have experience with the KZ. We shopped them when we bought the fifth wheel we have now, but couldn't find the floor plan we wanted in a short length (garage limitation), but, we were impressed with the quality relative to others in the same price range. When we were looking, the KZ had a 2 year warranty - better than most. Don't know if they still do or not.
You'll be glad you're keeping your G rated tires.