I don't happen to have heated mittens/gloves yet, but as an old guy, just in the last two years I can see their value: with circulation problems fairly common these days, these make good sense.
Down mittens seem warmest w/o heaters, but most of these no longer work on the coldest days for me. (Previously, I've had a great pair but almost never had to use them; alas, no longer.) And the Hestra, etc. warmest mitts w/o heaters are heavy, huge and bulky - they barely if at all fit inside pole straps on those coldest days.
That said, I found a work around for my own circulation problems. Last season, inside a pair of down or fiber mittens designed for warmth but still not bulky, and not super warm for such as myself, I put hands with two layers of extra thin, black silk liner gloves on already, in large and in extra large inside of one another.
It turns out this combination is warmer than the bulkiest Hestra, etc. mitts, by a lot. And it is not bulky at all. In addition, the silk liners come out of the mitts really easily, and allow for really fine motor tasks, like picking things up, adjusting masks and adjusting goggles, etc. without the silk protected fingers getting cold on those short periods out of the warmer mitt. (And they would thus work for smart phone stuff too, though I don't use them for that on the slopes.)
In my case, I took my n95v and/or surgical mask off while skiing and put them back on at the bottom for the lift line each run, and this was possible with this super warm mitten/double silk glove liner setup because of those layered thin silk liners.
The final bonus to this is that with three layers, one can come off if things warm up, then go back on if it gets colder.
(I was good to more than minus 20 degrees with wind blowing on multiple days last season.)
The one drawback to this setup that I have experienced is that the bare silk liners are at risk from velcro and such - it grabs them and starts to unravel/rip them, and would wear them out fairly quickly (one to three seasons maybe), if one is not careful. I had to develop routines that kept them away from the velcro, so that they would last longer. I anticipate that unavoidable contact with such velcro stuff will mean that every two to five years I will have to buy replacements, or at least backups.