I am contemplating getting some thermic heated insoles for the wife's LS Nepal Extremes size 41 in an attempt to enhance the comfort of my belayer. Until a couple of days ago I didn't know that these things existed so my knowledge on the topic is obviously very limited. Do they actually work? Which ones should I get? Do they take up extra room (compared to SuperFeet Green)? Is it a crazy idea to use in mountaineering boots?
I work in a shop that sells a similar product, we fit them to ski boots mostly but will be fine in other footwear. It's not cheap but it does work, it's all about stimulating blood flow rathe than warming the boot as such.
The set we sell has two options, a flat foam insole with a slot for the element which will be similar and replace the stock insole from the boot. Or the second option which is a thin protective cover for the element which allows them to be fitted to custom insoles or super feet if that's what you have in your boots already.
If you can get them fitted in a store as its a bit of a faff.
You should be able to fit them to mountaineering boots. Maybe take a bit of bodging to fit the battery packs somewhere, these would normally fit onto the outside of a ski boot on the powerstrap.