Meh. Against my better judgment, I downloaded it and poked around. Predictably, it does not play well others. Most notable, there is no export functionality. There is a 'Share as PDF' which is (a) not the same, and (b) broken for me because 'my email program is not set up properly' which is false. Hard to trust. (Evernote has a fine export capability, fwiw). One Note will, however, appeal to people who prefer 'struct…
I just want to chime in on how frustrating it is that you can't save Outlook emails in a standard non-mircorosft format that another mail client can understand (even Outlook on Windows) - apparently it saves it as ".olm" format (Outlook for Mac). Serious WTF here. For this reason alone, I'm still using a Windows VM simply for the "real" Outlook for work purposes.
The only problem I know of with this approach, when coming from Outlook, are the Winmail.dat files that Outlook (or MS Exchange?) creates "to preserve text formatting".