The somersault squat is worth trying for sure, nice twist on a warm up drill I do sometimes. Never saw this movement done this way before… cheers!
It is great without weight because you will get a nice burn in the quads doing them. Can be used as a warm up / activation drill like CC just said, activating the quads before more conventional movements like back squats etc. They remind me of these, toe touch squats.
CT did an article many years ago on squat variations, its worth a read.
Just to reiterate what CC said, you could potentially sacrifice joint health targeting specific areas (teardrop) using these methods but then that all depends on the individuals biomechanics.
I could never get the old style hack squats to flow as my arse always got in the way standing up lol. Sissy squats on the other hand with a plate held across the chest are great but time spent with no weight is definitely advised until you get your groove on with the movement. Siff lunges are also great esp. with the rear foot elevated like in the split squat.