Ok...

What is the problem?

Well, the coast guard would have a problem. the vest is not legal.
Zhik would have a problem and void any implied or stated warranty. The PR would be very bad for them.

His team mate might have a problem if the situation really sucks and he is unable to render assistance.

The Mark boat crew might have a problem in rendering assistance if they assumed his vest would perform as all of the other vests on the other sailors. So, they may not be able to help save his butt in some situations.

The guy's family might have a problem after the fact..

What about US... his competitors.

If he is a Hobie sailor.... he is violating the PFD approval rule. So he is breaking an equipment rule.

If he is a Tornado sailor. I don't remember a class PFD rule.

Where would you draw the line.