Anyone use them?  How do they work?

I have them and they work ok. They have two settings I believe and u have to recharge them after each use. They last a few hours not all day. If I had to do again I would probably just get some wool insoles from two tracks and spend money on the bestboots u can afford.

I hunt in a swamp, so I need to wear chest waders.  Just trying to find an alternative to hauling my pack boots all the way in and having to change.  Wondering if those big insulated over boot things work?

Yes, "the big insulated over-boot thingies" work. But for best results, you have to put them on before your feet get cold. The ones I have are not the giant sleeping bag type, but rather, more like a reflective emergency blanket with a little more insulation and Camo. They work best if you put them on as soon as you get to your stand on really cold days. They do feel a little akward to stand in though, and are not meant to be walked in.
I just picked up some of the thermocell insoles to try this weekend. They are quite thick, and only heat from the toes to the ball of the foot. Not sure yet if they'll work as advertised with my boots, as I had to remove the stock insoles to have room for my feet. I'll update after a few uses.

I have them. I'm not impressed. Plus they take up more room then the insoles so now you need a bigger boot.

So where did you you get your boot cover thingies.  All I can find are those giant insulated ones, don't how you can move your feet on your tree stand platform?

I think a company called artic shield sold the smaller boot booties for your feet. I also have the boot blankets for my wife she likes them and I just throw in a few feet warmers if she gets cold.

Hot-mocs is another option

I saw them and wondered myself.  Having suffered with cold feet for about ever, I hopped they would be great.  Guess I will save my money.  I use the heat packs, but they don't work the best in rubber boots and waders. Not enough air flow I think. I may have to get some of those big boot covers, but hate to pack one more thing with me.

Guys look up Thunderbolt electric socks. I have them and they work great. Not cheap but worth every penny

Best solution I have found in a long time is to use the Artic Shields over a pair of "Crocks".  Some thing about the crocks really warm my feet and the Artice Shield booties help keep them comfy for a long time.

I almost bought some electric insoles for motorcycle riders and a small motorcycle size deep cell battery. I know it sounds out there alittle. But staying dawn to dark at a stand( ground blind or treestand, not A box stand with Lazy Boy! ) does test your indurance. I went ahead and ordered some Icebrealers. Will try those first since everyone that has used them gave it A plus.