We use these with our kids (age 2 1/2 & 5 last summer) and love them for swimming. They keep them afloat better than water wings, but are less hot/cover less body than a traditional life vest. It also helped the 5 yr old to pop back up after going under water at the end of the water slide.
Think of it like a little lifesaver ring with attached water wings. I also think it is easier for the kids to sort of just hang out upright/tread water. They seem to need to be leaning forward or floating backward in traditional vests. One big thing is that it fits tight enough around the child's midsection. If it is too loose, I think it would float up toward their chest/neck area & not be comfy. And the arm ring part needs to be up on their biceps, not on the forearms.
I would not use them as a PFD which is expected to save the life of a young child who fell off a boat or the like--for that purpose I'd want the type that rolls the kid onto their backs & has the extra floatation piece behind their necks.
They are USCG Type III:
Flotation Aid
Usually the most comfortable life vest for continuous wear. Good for calm, inland waters or where rescue is likely to happen quickly.