Of course it would be game changing if it got to 99+% but I don't think we are there yet. If people don't take any other testing supplies and the watch isn't accurate, they they could go hypo easily especially during exercise and not try to remedy it until too late. If a single person dies trusting the watch's cgm it will be unlike any other testing device failing.
Perhaps same with pricking, if it doesn't correlate with how you're feeling test again, cgm can provide a guide and if in doubt prick. I still think at 99% confidence it would be game changing