Putting obvious freezing weather aside its what if it turns parky overnight we should be considering.
Well I have used Wickes and Feb Wintamix with good success. I have had two that did get caught and froze solid but are still there today. When I say solid is was white over with frost but under that frost it was probably ok. Feb Winta mix has air aintrainer that works from a set state but it also has an anti freeze in it that stops the water freezing so protection from wet to set. It also has accelerator in to get it set quicker.
Do we worry about our car radiator freezing? No we have confidence in the anti freeze and Winta mix has it in. Worked for me.