I think people uses fridges because they are readily available and they do exactly what you need well, holding a temperature, being cold or warm. I have a hovabator also but I am expecting 4 + clutches this year and 2-3 times that next season so i wanted something tested out and ready to go. I was set on having the glass door so I could see everything without opening the door. Every time you open it the temps can fluctuate.

With how I have it set up , the temps are rock solid. They are the same throughout the entire thing every time/ day I look at it.