They are legit, I tapped to one. People tap to them all of the time. My issue with wristlocks (the goose neck wristlock specifically) though is that I can't imagine somebody tapping to them in a high level MMA or grappling match. I have seen men break a finger during live rolling who only stop after they are done to then realize that they broke a finger. I'm sure you guys have seen it too, the gnarly dude at a gym who breaks his toe, wraps it with tape like a mummy, and then jumps back on the mat.
I've seen that gooseneck wrist lock compressed to the point where the palm is touching the wrist and nothing broke. Different strokes for different folks and some people are freaks but I just don't think that breaking toes and wrists is a "fight finisher".