How I Use It
I teach mostly Honors level freshman and junior English classes, and I use this kind of app for leading interpretive discussions. I connect an iPad running this type of app through an Apple TV and projector, and I hand-write questions and responses to questions on the app, which are then projected onto the screen. I also use an etext of whatever literature we're reading, and can use the highlight, annotate, and search functions.
I have tried many of these productivity/ notetaking types of apps, and have found pros and cons with each. Notability is cheap, has an appealing interface, and the audio and picture-snapping features are a nice-to-have, but not need-to-have, at least in my experience. The biggest con for me was the palm-recognition feature, and handwriting functionality, which I found to be lacking. After consideration, I have used the Goodnotes app, with which I've been very satisfied.