I life-guarded for almost 10 years, the only way I would ever let anything that supported a human floating __besides__ an approved life jacket was if the pool was almost empty (such that the one person got my undivided attention) and if I knew the child to already be a strong swimmer.
I highly encourage everyone reading this to not swim at pools that allow floats of any kind besides a life jacket, even something as simple as water wings. [0] It encourages kids to go deeper than they should, and if they fall off they're in big trouble. It creates the possibility for a child to get trapped under someone else, and a life guard has almost no chance in that scenario.
95% of guarding is preventive.
Neat site though.
[0] Water wings can create the situation where a child has their head underwater and their arms up above water, but they can't pull themselves up.