Nice execution, but not clear why you need so much adjustability, and what the finished assembly weighs relative to the OEM hanger.
I know that when I did mine I had brand new springs, so trying to put the spring eye in the right spot in the slider was a bit of guesswork and a little more adjustment would have been handy.
On a race car it would let you play around with different spring lengths or spring section lengths, especially if you had some adjustment at the front hanger as well.