I think Cobett's and similar waterers do what they are supposed to do - stay open in cold weather better than"regular" waterers without electrical cost.
My concern with all them is that I'm afraid they are designed for people more than for cattle. I realize the practical need to keep water flowing and the miserable hassle of thawing frozen waterers. But part of the reason these waterers work is that they have a limited opening or a barrier to keep the cold air out, and this limited opening can restrict water intake by the cattle.
Water intake drives feed intake. If we restrict water to cattle on feed, they will eat less and gain less per day. If we restrict water to beef cows, they will eat less and they can struggle to stay warm in cold weather. For fed cattle, we need 1 water space for every 25 head and for beef cows we need 1 water space per 15 cows. So, I guess they're fine as long as you have plenty of them.
I talked with both the Miraco and Ritchie reps at National Cattlemen's a few years ago, and asked them what the electric cost would be to keep a trough waterer open in cold weather and they both thought $35-$40 per year. I don't know if that's right, but at double that cost it still seems like cheap insurance to me.