John
It's early days for me using Onenote via Microsoft Classroom. Our authority has bought into providing staff and pupils with their own copies of Office and I have to say that so far I'm really enjoying using Onenote with shared class notes and individual pupil notes being used to provide assignment solutions as well as pupils own notes.
The desktop version of Onenote I'd definitely the best experience and it pains me to say do, but works better on PC than Mac.
I've had a few sync problems with notes not going to separate pupils which is a pain. The work around is to have the pupil log into Glow and pick up the synced note there, but I'd rather not incorporate work arounds.

Getting pupils to find the notebook in the first place is a real old faff, using involving logging into Office 365 and pressing the button to open notebook in Onenote. Once connected on the PC software app it's generally a very good experience.

On the whole though I'm very enthused by the communication and collaboration opportunities that Classroom offers (principally via Onenote).

A big thumbs up this far.