I think we could find a picture to support either view of concrete and plastic waterers. Neither of them are all the same - very major differences between manufacturers of both plastic and concrete waterers.

I have both and have had no trouble with the Petersen in the winter - other than adjusting the thermostat once in a while (it is very sensitive, doesn't take much of a turn of the screw to make a big change in water temp) over about 4 years.  I have had some difficulty with the plastic waterers as described above. They just are not as insulated in below zero F weather.

Here is a picture from January 2008 of my Petersen when the air temperature was about -10 degrees F.

I think in this sort of weather you are actually better off with a smaller waterer than a larger one for he number of head using it. I did change the float on mine from the ball to a flat type and it fills a lot faster which is important in the summer.

FWIW.

Jim at Dawn

(Waterer at -10 deg F.JPG)

Waterer at -10 deg F.JPG (82KB - 137 downloads)