PFDs should always be obligatory. Here's my favorite story about them. In the Coast Guard I did review of inspection reports regarding accidents. One occurred in Chesapeake Bay were a young couple and their infant took a small guided boat across the bay. The engine exploded. All died from drowning except the infant, who survived. The only one wearing a PFD was the infant.
SOS are easy to wear, you won't notice they are there.