In the last 20 years I have had four float tubes, actually worn out the first two, zipper failure on the first; fabric failure on the second ( which I patched and would not hesitate to use today, except for a slow leak). I was blessed with long arms which allowed me even with a round tube to reach over and put on my fins which is the safest way. I learned last year if entering the water with fins on pull the tube up under your seat, upside down with your feet and tube higher than your head is not a good thing.
There was an incident on the Hooch this weekend where some Boy Scouts may have saved the life of a upside down float tuber. Inhalation of dihyrogen monoxide can be hazardous to your health.