I wondered about this... I still am using an original Air Hawk...bought it in 2008 or 2009. My husband’s first Air Hawk R was very good quality. That cushion fell off the trike and the rear tire ran over it...ruined it. Bought another “R” for him in 2016... the cushion was definitely smaller and the materials were definitely not near as good quality as the first. I gave that cushion to a friend after Jim passed so have no knowledge as to how well it has held up. My original is still as good as new.
Thanks for passing this info along.