This is a terrible compromise, absolutely terrible. The rest of the dropbox notifications are actually useful, you know, like the "dropbox link has been copied" notifications that otherwise also go away when you disable notifications as a whole. What boggles my mind, is that you would sooner instruct us to disable all notifications, which makes dropbox worse as a whole, rather than just letting us disable the annoying one because you want to intrusively advertise your service. Just let us disable it - this feature is universally hated by everyone, and not a single person that uses the free version of your service will feel compelled to buy it, if this is how you treat them.
What makes the popup annoying? Well, first and foremost, it will literally interject itself over fullscreen applications, unlike literally any other notification on the windows 10 operating system, which all otherwise abide by the "game mode" criterion - i.e. no notifications if you have games running. To make matters worse, this is also the only notification that doesn't go away unless you press that tiny little arrow in the top right corner of it, because clicking the box opens up the "upgrade your subscription page". A notification should max display for just a few seconds, and then automatically be dismissed, why on earth doesn't it? So, if you're like me, you can be playing a game and have this stupid popup occupy the screen space that would otherwise be used for UI elements that you need. And if you click on it, with exclusive fullscreen, it focuses you to the desktop. Bravo dropbox