I use trapping skills all the time when i spar against Muay Thai or Boxing practitioners, and YES it does work and works well. They always come up to me after and ask me what i was doing because it is so effective.
The problem isn't the skill, the problem is that almost no one knows how to do it properly. Trapping skills work EXACTLY like Jujitsu skills. You have to think of trapping like stand up grappling.
You cannot try to "muscle" a move or you will get stuck. If you use your shoulders, you are WRONG, if your shoulders turn, you are WRONG. If you don't understand forward energy, you are WRONG, if you don't understand constant pressure, you are WRONG. High level sensitivity takes many many years to develop, just like a great grappler who can transition from move to move by feel alone rather than trying to force moves. Someone who is great at trapping, fights almost exactly like a high level grappler.
I have yet to meet anyone outside of pure Wing Chun who can do trapping properly. There are so many wannabe "trappers" who learn a few things but completely lack the structure or understanding of high level sensitivity. They then go and spar and get completely worked over. This is why the MMA community at large look down at Wing Chun and trapping skills.
Now, with all that said, here's the flip side to the coin. Trapping skills alone will NOT work in the cage or ring. You must have a deep understanding of pure striking arts such as Boxing, Muay Thai, Savate etc...
You must ALSO have a deep understanding of a pure grappling art such as Judo, Jujitsu, Catch etc...
Trapping is only good between Boxing and Clinching range. So getting there is half the battle. That's why it's important to know a pure striking art.
In other words, you should never rely on trapping but should incorporate it just like any other range or tool in your arsenal.
Hmm...i guess the best way to show or explain this is to actually put up a video of myself sparring a pure striker using it. I'll try and get one up soon.