One strong message of the movie is that "There is no secret". This is put forth through the scroll as well as the secret ingredient soup. From this I think we can figure that the Wushi finger hold is not really a secret.
Also, from the way Master Shifu uses it to induce fear in Po, it seems like a mostly psychological technique.
If you follow the fight between Po and Tai Lung, you could see that it is mostly Tai-Lung destroying himself with his own energy. Po merely throws back Tai-Lung's energy.
What the Wushi finger hold does is create fear in an already agitated Tai Lung who says that you are just a panda, you can't defeat me.
This fear coupled with the fact that Tai-Lung really "believes" in the existence of the Wushi finger hold, create in Tai-Lung a very strong belief that Po can destroy him if that finger moves.
The actual move is just a trigger I suppose for Tai-Lung to give his own body the command for self destruction. The skadoosh is probably to denote psychological destruction of the enemy.
Obviously, this is still an animated movie and the actual skadoosh was not shown, so we are all merely making interpretations.