Sporty's did a test of the X-Naut cooling mount with positive results. Here is a link to their article:
I use an iPad Mini 5 with a Pivot case clamped to the yoke horn. Keep it out of direct sunlight, especially while it is connected to power and charging. I haven't had mine go into thermal shutdown since I got the new Pivot case, which has more air flow around the back of the iPad.
Been using the iPad in flight for 10-years. iPad 2 was my first iPad back in May 2011. Never had one overheat in flight. Have only seen iPad in cases overheat. The case does not allow for proper cooling. Get rid of the case and you will get rid the over heat problem it causes.
I've had mine overheat, and yes, I do have it in a case, but not in quite a while since I've learned to keep it out of direct sunlight in the cockpit. My observation flying with a lot of clients who yoke-mount it is they have trouble keeping it out of the sunlight. I keep mine loose, with a case with a fuzzy back so it won't slide from where I put in (usually my non-kneeboard thigh) so i can move it wherever necessary if the sun is shining on it).