I used one for my ducks last year and it worked quite well. Of course, I only had 3 Pekins back then, lol. Now I have 26!!! I will have to pick up a bigger one this year. I used the smaller one (can't remember how many quarts) which will go in the chicken tractor this winter. I will (hopefully) be down to 15 ducks soon so the 5 gallon size should work combined with a rubber bowl and the heated hose for refilling in the mornings. It's hard to say if it made much difference on my electric bill, as I also had the heater for the horses water going part-time (mostly at night), the heated base for the chickens' water, and a new infrared heater for the living room going on, too, so my bill was higher than normal anyway.
With the electric bill, it's odd . . . I've replaced all of the lights with ICFs, started unplugging appliances not in use, made more effort to make sure lights/whatnot not in use are turned off . . . yet my monthly bill is nearly double what it was 2 yrs ago. My summer electric bill is generally around $60 (and that was before I switched all of the lights to ICFs - I did it gradually). Now a 'good' month is $100. I have propane, not natural gas, so that doesn't factor in to the Consumer's bill.