I dont think it works

Using the thumb to deviate an arm instead of the entire hand doesnt make sense. Allowing one to keep punching you while you just protect your head and lose sight doesnt work either. Karate offers more practical strategies for these situations. I guess later they teach chokes but if you dont trust the first lessons why get to the later lessons.

Veiga2012 about BJJ Brazilian Jiu-Jitsu Mixed Martial Arts Lessons, v2.5