I think many are confusing bouncing with jumping. When I bounce I never leave the ground and when I do leave the ground it is to simply to move forward, backwards, or on an angle. Even this movement only has me maybe a millimeter off the ground. You should be using your calves to bounce with not your knees. If you calves are not burning after a good workout then you have been jumping not bouncing. You may at time have some space under your toes, again maybe a millimeter or so, but nothing more than that. And yes there is some strain on your ankles but nothing debilitating. You do more damage to the joint with the kick, the impact of the kick, and the twisting for the kick than you do with the bouncing, just my view on it.
Again though I think this is best for the light skinny guys, for the heavy weights it uses a lot of effort to get an 18 stone or more body moving and to last throughout the fight.
PS a stone is 14 pounds.