Product review (1 stars): OK while they lasted
I will second another reviewer that said that these run small - they really do.  Someone with tiny feet would be OK, but I was only able to wedge the tips of my toes into these.  That was OK though, as it's only the toe area that is heated.  The heater got to the point of being almost uncomfortably warm, but since I could only wedge my toes in so far, that was alright.  I only used the heater for an hour or two for 3-4 days a week for about two months (maybe less) before I plugged them in one morning and one of the slippers was no longer heating.  Haven't used them since.  Might pull out the units in the toes to see if I can jury rig the wire around to work, but I'm not a huge fan of doing that on a heating element for the fire risk.

So I'd say these were OK while they lasted (they did heat, but the size and the inability to control the actual temperature were major drawbacks), but I couldn't really recommend them based on how short a lifespan they had.  So it's back to microwaveable slippers for me I guess!