Mightier app for building emotion regulation?

I saw a recommendation for the Mightier app and was intrigued. Has anyone else tried it, and did it help? 

I am thinking of it for my 7yo, who I am coming to understand as autistic (Aspergers). He melts down fairly often, such as when he can’t get something to work the way he wants, or when he bumps something and hurts himself. Once the meltdown starts, he often feels even more upset about having gotten upset—“wasting time” for the thing he really wanted to be doing—but he doesn’t seem to know how to calm down either. I’m curious about the biofeedback approach, but would love any other input on whether it helps. Other recommendations are welcome also!