It is about the purpose of the pump - generally speaking, Bathmate is marketed to men who can get erections but would like to be bigger or to last longer. It is also a lot cheaper than a therapuetic pump. Therapeutic pumps such as SomaErect, Farnhurst, etc., are marketed to men with ED who will need to use restriction rings for penetration.
Follow the instructions for your device rather than what you have read about other people with different devices.