These plugs are extremely well designed, Rather than being too slim in the overall design or expanding too fast just as it tapers off at the base, these have been designed to be in a nice comfortable ball shape.
These are great for guys practising to take a fist. The necks are the correct length to make sure the bulbous area moves deep enough in to the arse area for comfort and therefore allows the ass to relax around the base of the neck.
Place one alongside a fist and you'll understand how this design is unique and perfect for working up to a fist or keeping the arse open in between play sessions.