The App Store version means you don’t have to have the ****** Microsoft updater app running constantly as a Launch Daemon.
But it’s the only way to access the other stream releases (effectively the beta and alpha testing versions of Office).
Plus, I strongly suspect (but haven’t checked) that Microsoft will release the latest releases via its own updater, and then take their sweet time updating the Mac App Store.
Orice 365 on the Mac is still at the stage where key features are being added everyday, so getting the latest release can actually be important.
Incidentally, people saying that you can get a lifetime purchase for a cheap price… At its best this will be the non-cloud version of Office (and did Microsoft say this is the last year they’ll be making non-cloud releases?).
So you won’t be able to share files with others via OneDrive (unless you pay for that separately), and you get limited updates (usually 12 months). To me, cloud docs is the whole reason to use Office. If I didn’t need that I’d just use Libre Office or Pages/Numbers/Keynote.
And in some cases these cheap versions of office are actually some dude selling a seat on a site license. These work but obviously if the dude moves on then his site license stops working. And if Microsoft finds out they turn it all off anyway. I’ve had a few friends burned by this.