Those M-Blocks are really clever, the way they move the reaction wheel around to allow it to simulate having three wheels when it has only one. But that limits the 'balancing' capability, though that's - for a cube - mostly a gimmick as far as I can tell, the locomotion capabilities are far more useful and they seem to do that just fine.
There was a popular mechanics article a many years ago about a box that moved without any outward visible means of locomotion. Inside it were a slide with a little tin can and some metal balls, going one way up the slide was easy and nearly friction free, the other way it released and fell, then bumped into a stop at the bottom which was enough to cause the box to slide a bit. That was mighty impressive when I was a kid, this is like an SF version of that.
There was a popular mechanics article a many years ago about a box that moved without any outward visible means of locomotion. Inside it were a slide with a little tin can and some metal balls, going one way up the slide was easy and nearly friction free, the other way it released and fell, then bumped into a stop at the bottom which was enough to cause the box to slide a bit. That was mighty impressive when I was a kid, this is like an SF version of that.