I don't use the auto brightness feature. As you mentioned, it does consume more battery because it's adjusting the brightness to settings that might not be necessary. For example, having the brightness set all the way up may not be needed when 75% of the setting will suffice. This occurs through the range of settings auto brightness adjusts to. I prefer to keep it set to a predefined setting that I know works for me throughout the day.
Also, you are using an app when the the Note 4 (all Android devices for that matter) do this without relying on an app. So my suggestion is to delete the app if you are using one and stick with the built in setting.