It would be as cool as watching nazis exterminate jews. If you want it in a war context, as cool as the nazis repressing the Warsaw ghetto uprising.
Just senseless massacre by a superior armed force.
Again, that is something we can see footage of already. The Mongols have an almost mystical quality in the eyes of most history fans, actually seeing them in action would be incredible. "cool", was defeinitely the wrong choice of word, but you can't deny that it would be interesting.