The problems are more:
1) If it is high enough to be effective for higher shots there is a very real chance of it actually knocking the incoming higher and into your own face. Of course with the correct timing this shouldn't happen but even then it means leaving your arm up a long time and therefore exposing your ribs/even chest.
In TWC, we step and turn so that our wrist is still at our center, but our center is now facing the side of the punching arm. This allows the punch to travel where our head WAS but we are in the clear on the opponents blind side...and our bong can be used to deflect/redirect or sense the next move, while the wu hand can now lop, trap, etc. to set up for the strike from the blind side.
I would not stand still and raise a bong sau to a punch coming straight at my face as a "block".
Aut Pax Aut Bellum - Either Peace or War