I quite fancied something similar,having seen several advertised , so went to look at one in some tackle shop.
IMO it looked and felt as though it was designed for a 12 yr old. Size wise I could not see me sitting comfortably on it at all, I am not huge at 6ft and 14 stone, but really it was a joke. The bag design was shocking, meaning every time you wanted something out , you had to stand up and rummage about under the seat . It felt not at all fit for purpose.
I really think there is an opening for a manufacturer to make something a bit larger than the above, but a bit smaller than the current batch of chairs that are available. There must be a better way of attaching a decent bag to the chair so you can clip it on and off for easy access whilst you are sat waiting for a bite.
I have started to use a simple bag with my veteran Chub Rover Chair , the bag clips onto the chair and the chair has its own shoulder strap.
I would like something a bit better but until something comes along the Chub chair and bag will do fine.
David