I used to have a bird bath heater in a bucket that I put vertical nipples into (forgive the bad sentence structure!) It eventually rusted and I replaced it with this unit which I bought. It has the horizontal nipples. I did not have problems with the chickens learning how it worked. I only used it in the winter in NJ. With the vertical nipple waterers, their combs get wet and that is a problem with frostbite.
https://www.premier1supplies.com/p/heated-poultry-waterer?cat_id=227

https://www.premier1supplies.com/p/heated-poultry-waterer?cat_id=227