If you're willing, don't be afraid to try the standby line, at least during testing days! The really great CMs told us repeatedly we may not get in (they don't want anyone to be disappointed), but having nothing else to do, I didn't mind trying my luck (and my great husband will do whatever I ask of him). Most guests, when they heard that, didn't even bother waiting, so there were only about 5 families waiting in standby. They let in 3 families, and then is was just us and a family behind us. I heard one of the "suit" CMs tell one of the "costume" CMs that they wouldn't be able to take us, and to remind us that there were no guarantees. But the great CMs kept asking, saying, it's just two more families, they won't take long, and finally got the go-ahead to let us in. I thanked every single person I walked past as they were letting us in, because I knew they didn't have to do that! But it sure did make my day!!
Most guests walked by, said, "Oh, it's that new princess, whats-her-name" and kept going. I do predict it's going to be PACKED once the movie comes out next month, just like Tangled was, once Merida's name becomes more well known. I didn't expect to have the chance to meet her until October, since I only get to the parks on Saturdays and waiting in the hot sun during the summer doesn't appeal to me too much.
Having done it once, I'll definitely do it again once I've seen the movie and have more to talk about with her - I wasn't sure what to say or to ask, since I know only what's been seen in the commercials. It was great that as an adult, I didn't feel rushed or hurried, she spent as much time interacting with us as she did with the kids, which I really do appreciate. (The Tangled play-and-greet was much the same.)
All in all, I'd say it's a must do!