Imagine it car sized, and running on a serial-hybrid power plant (electrical for sprints, turbo diesel that spins up while it "rests" to recharge its battery for sprints).
I'd be terrified even by a little one(consistent with the current size). If it had teeth, or that spinning balance beam had blades on it and they get maneuverability down...boy. Here's hoping DARPA doesn't fund the project to turn it into a weapon.
(edit: just to be clear - i can't run anywhere near as fast as usain bolt, so it wouldn't have to be ostrich or car sized to catch me)
It's also much larger. I imagine once they scale this up, it'll go even faster.
Can you imagine how frightening it would be to be chased by one of these things?