Not quite as good as you think. The save for Leia's Commander Effect is a 16, not an 11. So it's only a 25% chance with one roll, and about a 38% chance with two rolls, if I'm remembering my math correctly. Two chances at a 25% possibility, do not add up to an overall of 50%.
Still though, having the Force Point to re-roll isn't too bad, it's just a bit gimmicky. You will find some games where it does great for you. A guy at GenCon last year played Leia HC, the Ithorian, and a swarm of Ewoks. In the game I played against him, I think he saved a total of 7 pieces throughout the game. Of course, I've also played a game where a guy had Leia HC and a slew of Rebel Snowspeeders (it was 500 points, EPIC format) and he managed to save 4 snowspeeders in one game. I still ended up winning.
The problem is not whether the idea is sound or not, it's just tough to build a squad with enough power and other synergy to work good, even if you don't get the saves from Leia. So, like I said, sometimes it will bite you in the butt, because you won't save any pieces at all. Other times it will annoy the crap out of your opponent because they can't kill a single thing.