I would love squatting on a spring mat, since the potentiation effects would be nuts, but the upside down bosu ball I found fatigued my quadriceps extremely quickly, because they had to constantly apply force in transverse planes, wayy before I reached the bottom of the ROM and began to lift myself vertically in the frontal plane. That wouldn't be optimal for vertical jumping since it's all about the vert. Still even with bodyweight my legs shook considerably, I felt incredibly weighed down as well. But that don't mean it don't work really, Ithnk a springmat is better to keep the forces in the frontal plane
