I think they made the right call blocking off the USB-C charging port. Any extra heat from charging the battery would not be good. I'm hoping they really have fully tested it for heat management, because that's always been my fear of these grips that I've seen online that people have 3D-printed. I'm willing to trust them enough to toss in $15, as I know that Jeremy Parish is good people, and Fangamer is big enough to also deserve some trust (as opposed to this being a Kickstarter set up by some clown no one has ever heard of).
Yea, I don't know how they tested heat either. If they're just using external IR measurements, it's not going to prove much.
But on top of that, it could be easy to cover the little bit of air flow in the case.
Or any potential joycon interference (due to not being electrically connected, like when you connect directly to the Switch.
Or being unable to play for longer than ~3 hr stretches at a time.
Like I said, interesting concept, but I feel like there will eventually be a version that's more than just plastic. More like an adaptor.