As a new member, I'd like to introduce myself.
I'm a jazz guitarist/composer. I taught at Berklee for 25 years. I've been using Notion since it first came out. I use it mainly for writing instructional pieces for guitar, lead sheets, and so forth. I have the Rhythm Section package. (I'll post some links to some of my Notion guitar pieces, in the Audio Demo forum.)
I'm using Notion in my jazz seminars and workshops, and in my private lessons.
I used MusicPrinter Plus for many years. I worked with Jack Jarrett when he we were both at Berklee, and I wrote some music education software that read MusicPrinter Plus files, did chord-scale analysis, and stored the results in a database. Of course, when MusicPrinter Plus went under, my application had limited use. I was thrilled when Notion came out, with the promise of MusicXML, because now I can export from Notion and my program can read and analyze the MusicXML. Well, there's still one problem: Notion's MusicXML export doesn't include chord symbols. I can work around that by editing the MusicXML by hand, for now. (I also wrote a program that creates MusicXML from my old MusicPrinter Plus files, so my program can use that.)
I hope that Notion will soon add chord symbols to the MusicXML output.