Harness/hip lifts (advanced form of belt squats) are an exceptional movement and huge weight can be lifted...1,200-1,500 plus.
More strength is generated when a weight is lifted from below ,or at the hip line ,than if that same weight was placed on the shoulders; squat position bar on top of the shoulders or placed in the front squat position. A lifter is taking full advantage of his potential strength like never before. with harness lifts.
When lifting in a harness lift, it's pure, raw strength of the hips, glutes and chain of leg muscles all the way down to the feet. Can do 5 reps of squats with 400..than might be doing 500-550 with a Harness belt with that same 400lbs..
I still prefer the BB Hack squat over regular DL's. The weight is in a more natural line to be lifted, with the bar behind you, knee's not in the way and body not over extended leaning forward. . Nothing against a trap bar, used many versions with good results. Also for overhead pressing, hi-pulls, etc.
Good Luck.