Re: Float tubers....ASSEMBLEEEEEE!
"what happens if you have a big sudden 'leak' and go flat..........just swim for it ? Seems risky."
I've been tubing since I was 15 (57 now) and have always used circular tubes with rubber inner tubes. Many times we had leaks where after a few hours it might be a bit softer but never a single complete failure. However I've always done it when the water was warmer so we could just swim.
These newer ones with plastic bladders conceivably could have a complete failure but the bladders are pretty tough. Almost all have multiple bladders so you'd always have some flotation. I have a friend who puts carefully cut pieces of pieces of the foam "water noodles" which are like foam pipe insulation. This can give a bit of a "lumpy" shape but will give floatation in an emergency. We also put about 10-12 inside our kayaks for same reason.
A PFD (personnal flatation device) is of course wise.