Are they using HN's now?
If not, get them started asap, it can take time for them to get the hang of them and you don't want to do that during temps extremes.
I have used this DIY heated waterer for 5 years now, very happy with it.
https://www.backyardchickens.com/articles/aarts-heated-waterer-with-horizontal-nipples.67256/
I currently use a metal double walled 3 gallon waterer. I purchased a metal waterer heating plate for the winter. My chickens have not used HNs, so I guess maybe I should build a bucket and see if they use it.
I was surprised to see you using an aquarium heater for your waterer. I did not think they would last very long. The other articles I have seen use a stock tank heater, which I believe is made for larger animals in a larger tank and the heater is much more robust. But maybe with only a few gallons of water, the aquarium heater is good enough. I also noticed that the first aquarium heater you got failed in a short time. How do you know which aquarium heater will work (design, wattage, etc....)? I know you updated your article with the heater you currently use, but I don't know if that model is still available after 5 years.