I guess I am a bit old fashioned, but I want the ability to trap gas on either side of the wing. If one side has a puncture, I want to be able to manage the trapped gas to maintain my buoyancy.
Now, I understand that most (if not all) of the manufacturer's have designed the back portion of the donut so that it is possible to trap gas in either side, but no matter what...the pathway exists. Which means the chance of the gas to accidentally travel to the other side and vent through a puncture is still there.
Since I do not have a problem with unwanted gas trapping (which is what the donut solves), what benefit is the donut really bringing to the table?
In truth, this probably boils down to 6 of this, a half dozen of the other. In the big scheme of life, donut vs horseshoe ranks down there with bcd inflator hose...inside or outside of the bungee.