It's a solid game, well worth the time to play through. It's slightly shorter than most other JRPGs I've played, but it's very stylish, has a unique feel, and has a pretty solid action battle system (Viola is awesome, by the way).
I played the PS3 version. I haven't looked into it, but if the "extra characters" mentioned above fall into the categories I'm thinking of, you probably won't use them anyway because they show up or become playable very late in the game. That said, I had no complaints about the PS3 version and I don't really care about trophies. In fact, I find them distracting sometimes in a story-heavy game.
In short, definitely worth $15 if you're a fan of JRPGs or even classical music.