Flexible spine
I had always thought the key to Cheetah speed and movement was the flexibility and energy storage properties of its spine and sinews in the back, The MIT beast looks extremely rigid and although I know they are talking about 'stamping' harder to achieve lift and time off the ground, it sounds intuitively inefficient energy wise.
The flexible spine is also a key to agility in the natural world, for the kind of super fast rough and tumble moves a cheetah uses in hunting without flexibility in the spine means finding alternatives ways to stabilise at the legs making them more complex and potentially weaker.