Used this device on my submissive. At first she thought she could take it with no problem, but I could tell she was a little scared...by the time I finished, she had used her safeword and begged me to stop with a sniffle and tears in her eyes! The flat chest piece helps keep it balanced thus preventing it from twisting and making sure her nipples were evenly stretched!
PS. She had so much fun I might have her use it on me!