https://joeveo.com/pages/the-temperfect-mug
I've used one daily since 2015. It's excellent. Gets a coffee to the right drinking temp in moments then keeps it there. No charging pads, controls, etc. Just works. Best thing I've ever backed on Kickstarter.
One thing the Joeveo does do is bring the temperature down from "are those blisters on my tongue?" to a reasonable temp relatively quickly. What it doesn't do, apparently, is keep drinks hot for very long. I've only used it a few times so far, but one Saturday I took a mug of Joe on the drive to a club run and drank about half of it on the way. Came back two hours later, and the coffee was lukewarm. It's a double-walled mug, any other double-walled mug I've used for this exact use case results in reasonably warm coffee when I get back. The only difference is that the Joeveo has the PCM layered in there. (And the $200 Ember travel mug would still have 145F coffee even after several hours.)
I had high hopes, and I'll keep experimenting, but so far the Joeveo mug has been a disappointment. Thankfully it was "only" $50.
For instance, the lid didn't have enough threading, and as a result would spill coffee. I don't know if they've fixed that, but it was clear just from looking at it that it needed more threads.
Travel mugs are just far more unpleasant to drink out of, and when coffee is about 140 degrees, I don't find myself spending hours sipping at it. It takes me about 5-10 minutes to go through.
A heavy mug already perform this task alright without the clever phase transition, but I drink enough coffee for it to be worth $100 to slightly improve the situation with a mug with the wax tech in it.
It seems like it would just muddle the temperature down to mildly above room temperature over multiple minutes. So that the drink and material are the same temperature but the material holds heat due to being insulated on one side. What this would mean is the mug would get less effective as you drink more.
The insulated mug would make the time longer but it is no where near something like the Ember that converts electricity to heat.
Seems like KS schlock for people that don't want to think about if / how it works.