One of the issues I was told of when I bought mine, was how far down the chest the strap around the back is. It is important that the strap be on the ribs, not below the ribs, in order not to cut into the person as they are suspended in the water.
The SOS length is a bit shorter than the
Mustang, and is what we choose for my early teenage daughter (5 foot height).
Be sure to get the Coast Guard Approved models, apparently the manufacturing QC is significantly higher.