The problem is that TMI was NOT a really bad disaster. It was frightening, and could have been bad. Actually, though, it was quite contained. But the more reactors you have, the greater the chance of a really bad disaster. If one of these is small enough to be thrown around by a tornado, you have new possibilities of a really bad disaster. (I didn't check. I assume it's too heavy. But perhaps it could be broken open.)
OTOH, smaller reactors have a smaller "worst possible case". I'm not really convinced that they're a good idea, but I could be. (If it's intended for use in space, what happens if there's a catastrophic launch explosion? That might be a good use, if they can handle the heat, but I'd prefer that the fuel be mined on the moon.) Low probability accidents that are possible WILL eventually happen. (Or at least one should plan that way.)