I absolutely hate the new design. The whole point of the tabs was to increase the available screen space.
The MAC version of OneNote is already a very weak and sickly version of the Windows desktop version (which I unfortunately have to use at Work). Some of the core functionality which has sustained me as a One Note user for 15 years is not available - Automatic
saving of emails, to-do tags not being searchable etc and others not working as originally designed - copy link to page not displaying all the characters, Links to Documents not automatically book marking to the paragraph.. etc
Although I recognise the Mac version of One Note is a different beast from the PC version.. the very sad fact is the product management on OneNote since the release of OneNote 2013 has been shocking. A total lack of understanding from Microsoft's side about
how OneNote is used effectively in business/research etc, and what makes it a differentiator in the market (and lets be clear EverNote is so basic compared with OneNote 2013).
So to the straw-that-broke-the-camels-back...
I can't believe you are now forcing people to change the UI. I have been using oneNote since the 00's and the idea of having to use the, frankly terrible, Windows 10 interface will mean I am likely to stop using One Note.
"We've refined the experience in OneNote based on feedback from existing customers who have asked for a more consistent navigation model for organising their notebooks, sections, and pages across devices."
... I do not believe this! If you are a laptop or Desktop user, you would not choose to lose enhanced functionality for the occasional times where you need to access a document or a note from your mobile phone! I have
no idea who your "existing Customers" were but they are not representative of powerusers. your customers are not a homogenous group, there are multiple persona's each with a different need from the product. This is basic Customer eXperience 101.
I used to be a massive advocate, but I am refusing to upgrade to a hobbled, gealded version of OneNote. To add insult to injury I am constantly pestered by my PC about upgrading!