Disclaimer: This is just an opinion, not a judgment. Do what you think is right for your kids.
I spent my youth teaching swimming and as a lifeguard. I was also a swimming coach for a number of years.
Lifejackets are great but Water Wings are not always as safe to teach someone how to swim. It makes their arms float...not their head and body. It also makes moving your arms more difficult.
I remember plucking a dad and his child out of the deep-end who were lulled into a false sense of secuirty by water wings. The 3 year child had wrapped his arms and legs around the father's head and was drowning the adult.
That being said 1,000s of kids use them, I am sure without an issue.