I think box jumps are a little safer and just as effective.
M.Ed. Ex Phys
I have done squat jumps before (using 40# DBs), and I noticed a big increase in my vertical jump. So, IMO, they are a good tool/exercise to build power.
box jumps and band squats would be better for speed development and power than jump squat. The band squat is basically the same you just dont leave the ground and you dont have the impact on the joints.