For a raw lifter the hardest part is a few inches off the bottom. I cant figure out how youd set up chains so that most of the load comes on at this point. Deadlift i can see because you have the double weakness but with bench and squats it seems most of the load comes on too late in the ROM. So i still think pausing and reps would be more effective
On the chain thing, which has it's limitations, and this idea is as old as dirt:
Only useful for squatting, as the barbell is lifted off the ground, the length of chain, which needs to be significantly heavy adds to the weight of the bar, from nid-range to standing fully erect the moment arm (resistance) reduces dramatically, the chain adds weight to the bar adding resistance the further one approaches the fully erect position, wherby most of the resistance is being supported by the bones.
In this case finding a good leg-press ensures that the muscles resposible for squatting are exercised in a proper manner:
1.a rotational form of resistance, rotating on a common axis with the involved joint of the body.
2.an automatically variable form of resistance that varies instantly as movement occurs.
3.balanced resistance that varies in accordance with the actual requirements of the muscles in different positions.
4.resistance that is provided in a stretched starting position; which requires a range of movement in the machine that actually exceeds the possible range of movement of the user.
5. negative work potential
6.positive work potential
7.pre-stretching; a factor that is required during the last one or two repetitions of a set of high-intensity movements
8.resistance that is provided in the finishing position of the movement, the only position of full muscular contraction