I used these before for my handicap son.  The cut out for under the arms is a great improvement. They keep him a float with our supervision.

I can't swim so I took them on my trip to Mexico.  They worked well and kept me above even the big waves. They were, however, larger than I expected. I got the smaller of the two (yellow size medium) and they are huge. They took almost half of my suitcase. Imagine a plate that's as thick as a new bed pillow...well that's one of them.  And the arm holes are kind of big too. They stay on in the water, but they easily fall off when you stand up. I guess theye make them big enough for male arms. I'm about 135 puunds.