Microsoft did a similar thing around 15 years ago, where they got OEMs to preinstall a limited, ad-supported version of Word and Excel 2010 with new computers. They discontinued it after Office 2010, probably due to a combination of the feature set being enough for most people and the advertising not doing too well (I only recall seeing ads for Microsoft products) so I'm surprised they're bringing it back. I suppose the new limitation of not being able to save files locally is a big enough hassle to get most people who aren't just using it to view existing files to pay.
Apparently it is Windows-only and you can only save files on OneDrive.