I tried my new Boot Gloves at Loon Mountain in New Hampshire yesterday. Temps were in the low teens, I think; cold enough to need my face mask, anyway. Here's my report (with Head Vector 115 boots and Smartwool PhD Thin Cushion socks):
1) I wear an 8 1/2 mens shoe; my BSL in 297mm. So, I got the Mediums. They were pretty hard to get on - very tight - but once secured, they fit well.
2) My boots were warm when I put them on.
3) No issues stepping into the bindings.
4) On the hill, my feet were neither cold nor warm, which is how they usually feel. So, I can't really say how much effect they had.
5) I took them off at lunch and didn't bother to put them back on before going back out.
6) My feet (toes) felt pretty much the same, but it may have warmed up a few degrees by then.
So, I don't know what to say. Maybe I'd need to put only one on and compare how my feet feel. On the other hand, there's really no downside to wearing them - I don't mess with my buckles once I'm out on the slope - except that a female friend in our group kept referring to them as, "Tom's boot condoms," so if it's in the single digits or lower I'll try them again.