No need to justify your purchase to me mate.
And of course ramp angles are classed as adjustment...
Avanti use ZF differentials, I dont believe they are a copy of anything.
Plate size is smaller, so likely the clutch pack wont last as long, or have the same torque rating...but they seem to be doing fine on the clio scene.
Other areas to consider which will account for price difference are materials, treatments, machining tolerances, all account for overall quality and longevity. Im not saying Gripper is necessarliy less quality, but there is probably a good reason why a Sadev unit is 3 times the price.