This is a game changer

I would live in a constant terror while waiting because it looks like it could fall and ruin both bowls.

Would probably cook faster separately. If you do both it wastes energy, and more importantly time, heating the cup. Also you won't get even heat distribution with that set up. One part will probably still be cold unless you stop to stir every 30 seconds or so, but that would also waste energy/time to reheat the inside of the microwave.

what if i dont have bowls like that