Hi! Concert pianist here, have done arranging with software. From what I know of Notion, it’s excellent for both beginners and pros. I have used Finale, but find it clunky and just not as intuitive. Notion 6 is on my iPhone and I’ll be getting the full software soon; a DAW (digital audio workstation) called Studio One works with Notion. I tried the DAW called Pro Tools - supposedly the best in the biz - about 3 years ago. Trust me when I say it’s NOT for beginners. And a huge pain to set up. Sibelius is another writing software option that is intuitive I think, but made by the same company as Pro Tools and def more expensive. I’m taking lessons in composing and tho my teacher uses the well-established Finale, I’m sticking with Notion. Hope this helps, wishing your son the best of luck!!