Mine have worked well so far but we haven't had EXTENDED low temperatures so the jury is still out. On the nights that it has been in the 20's, any water that was in the bottom of the cups does freeze. However, usually the level of water is so low that it doesn't stick the nipples down.
Here's what I've done - If I'm around the night before I just turn the little cups upside down to empty any puddling water out then turn them back upright. (The amount of water is so small it won't make the litter too wet!)
My main concern has been that the water in/near the neck of the nipple would freeze inside and lock up the nipples. So far that has NOT happened. I keep a bird bath heater inside the bucket. I try to keep it close to the place where the cup waterer screws into the bucket and I raised up the heater to the level of them by putting in a glass pyrex bowl turned upside-down in the bottom of the bucket. Then I put the heater on top of that and try to keep it pushed toward the openings. (I'll post photos here later when I'm home from work.)
