Personally, I'm a skeptic for certain items, whether there's a rational basis or not.
The OP asked for opinion on a used lift kit. My response is "If it were so good when installed as new, why would it be for sale now?"
I've spent a lot of money over the decades trying to save a buck or two in the wrong places.
The suspension is a high-stress critical performance set of interrelated parts that must function well both individually as well as a total unit.
I'd always feel uncomfortable with this kind of used stuff even if it worked right...for a while.
High stress mechanical parts of unknown quality with unknown amount of prior use on top of unknown reasons for removal from prior Jeep...too many points for me to worry about.
get in--buckle up--hang on
"soothing agricultural implement/personal servant/Walter Mitty multidimensional access utility device conveniently travels on pavement when necessary and often keeps me warm/cool/dry/soothed as needed."