Monkey grip isn't about efficiency, it's about cool. Seriously, wouldn't you feel at least a little threatened when somewhen comes at you dual-wielding greatswords?
No. If I saw someone holding a sword longer than his body in each hand, I'd tell him he got lost and is in the wrong game. This is D&D, BESM is over thataway.
It is completely unbelieveable. I'll give that it isn't really broken, as you lose the 1.5x strength modifier. I actually hadn't considered it long enough to really think about the ramifications.
Monkey Grip and mercurial weapons are the silliest things in S&F, and its amazing the people that seem to think the two of them together are a good idea.