Perhaps I am missing how awesome this edge actually ends up being, but it seems odd that it would be more expensive then ones like footwork and possessive. Is the cost intended to be so high for such a small niche skill?

I think it's probably pretty fair. The niche-defense stuff isn't usually that expensive in that, in any fight in which someone isn't trying to kick you, Footwork is entirely useless, and even in fights where someone is trying to kick you, they likely still succeed -- just a little bit less often. Whether Desperate Improvisation can be used in a given fight is a little more in your control.

And don't get me wrong, it's a gimmicky edge but it's a potentially really powerful one in the exact right situation. Granted, in that situation maybe you should just be running away instead, but if you didn't, you might just kill everyone and walk away looking like a boss.

Then again, I might have thought it did something else at the time.
I think the helpfile was unclear at the time.

Anyway, the way that edge is worded it could be very nice. But honestly the helpfile is very unspecific. So, I'm not sure what it does beyond making it so you can use that skill (which is hardly ever used) and use it blind. I did not take it with my last savage for sure.