I had two occasions when water froze last year, but it only froze in the pole hose, putting the pole hose in a bucket of warm water was all that was needed. I have one of those little fan heaters that come on when the temp drops to freezing, it's on a long extension lead. the water doesn't get a chance to freeze before I get to the job, keeping the pole hose off the ground helps prevent freezing.
I may give that stuff a try this winter, just put some into the first two containers, it usually warms to above freezing by about 10 am.