I have Trigons on both my drysuits and would put one on my next suit.
The Trigon has 2 check valves. One keeps water from outside coming into the body of the pee valve. If that one failed, water could come in, run through the pee tube and come out the end of the pee tube. If you're plumbed in, that's not really a concern. I use a dry break female QD on the end of my pee tube, so if I'm not plumbed in, nothing in that line will leak out into the suit.
The other check valve is what allows air in the suit to equalize into the body of the pee valve. If it fails, urine in the pee valve body would leak into your suit.
For outside water to get into the suit, both would have to fail (or come out the end of the pee tube).
Or, of course, water could come into the suit by going around the pee valve. But, that is true for any pee valve.