Yikes, that's expensive for a bucket heater. Try this:
http://www.farmandfleet.com/product...sion-bucket-utility-de-icer.html#.Ugz5DbUo4iE
That's the one I bought so I can vouch that it works great. My bucket hangs inside an uninsulated and well-ventilated coop so it's out of the wind but it's cold in there. I haven't had any freezing at all with temps in the teens. Now, it says not to use an extension cord on the packaging but I do. I just chose one that was rated for outdoor use, thicker than the wire on the heater, and has a grounded plug. I made sure the connection is in a dry location.
I refill my bucket as needed and wash it with bleach maybe 3-4 times a year. It doesn't get slimy at all. I made the air hole tiny and the lid is on tight so no dirt gets in. And then the little stinkers drink from filthy puddles when they go out to range...
Oh, and they also fail to mention that you need to slide the small stopper up the cord to compress the chew protection coil until it is above the water line. Make sure you do that or you'll have rusty metal and orange water.
ETA -- I have 3 nipples for 10 chickens and it's plenty. I was advised not to go overboard on the number because lack of use can cause minerals to build up and cause leaking.