I've had these glove liners for one full season now (Minnesota!). They work very well! I normally just run them on low, as I only need my hands to stay a nice neutral temperature. Not numbingly cold, not overly hot/sweaty. If I haven't turned these on at all, and my fingers are getting numb, it only takes a few minutes (if that) on LOW to warm them up. I have tested these on the highest setting (too hot for me most of the time unless fingers got numb from not turning them on yet). I have also tested them with one glove turned off, and one on, and there is always an obvious difference. I have also tested them without wearing an outer glove over them. They can still keep my hands warm in a pinch without any outer gloves, but they are truly liners, and do not have the bulk of big winter gloves. Nor do they have the typical leather palm/finger protection that a typical outer glove would have (and I wouldn't want the extra bulk of this for something meant to be an inner liner).
Since you are putting these gloves inside another pair of gloves, you may need to have a bigger size for your main outer gloves. If you're existing outer gloves are already snug without liners, these may make them too tight. In my case, I can still use a few different types of my outer gloves.
My only gripe with these liners is that the gauntlet where the battery/switch are located can get a bit bulky, as I have to tuck these liners INSIDE my jacket sleeves and it bunches up against a wrist watch. My main outer gloves go outside of the jacket sleeves. With the these liners, the on/off button gets hidden under another glove and a jacket sleeve, so it is harder to check/adjust the power button to see if the power is on, or what level it is on (LED color). I do find from time-to-time that I've accidentally shut a glove off, or changed its power setting to a different level. I am getting pretty good at turning these on/off by just pressing through my jacket sleeve, without having to take the outer glove off or push the jacket back in order to physically see the button.
Having said all that, I still find these liners to be fantastic, and would buy again in a heart beat. They fit me SNUG (and SHOULD BE), but they are also a bit stretchy like a thicker spandex. Since they are a LINER, and not a true glove, I would expect them to be more snug, or else it would be even tougher to fit outer gloves over them. But buying just the liners gives me the freedom to choose from various outer gloves, or switch to a dry set of outer gloves.
