Ask IH: iPhone app's business model/pricing

Hi, guys. I'm just finishing my new side project. It's an iphone app for music composers. The app makes the creation of harmonies (voice leading) completely automatic saving too much time of work for them. We've running a custom algoritmh behind the scenes :)

The thing is that I'm not sure what should be the app business model because the app is for a very specific problem and niche. I was wondering what could be better, charging them just for donwload or make a fremium model.

What do you think about? I would like to read opinions for people outside the project :)

P.S: if anyone is a music composer and think that the app could be useful for him/her let me know ;)