In MoP, will IWT cause a hunter to turn?
On the live servers, pressing IWT will cause the hunter to shoot (and continue auto shots) against anyone within their firing radius...
But will not turn the hunter at all, meaning you don't shoot someone more than 90 degrees off or who is behind you.

If you can IWT, which will turn your toon to a melee who is swarming you, ala Rogues in duels...
Then you can deal with melee and still shoot them.
But if your IWT will not turn the Hunter, like most casters you're going to lose a lot of shots.

Instant is nice; use on the move.
And if your IWT is spammed, and it turns you, that's going to be great.
But if IWT will not turn your character... you're basically going to want to avoid melee range like the plague.
I'd think ranged is preferable anyway, because you're dominant at range... and melee toons are particularly bad against you at 30 yards.