"There is an important consideration there - not every App should have "the folder" removed on uninstall - it could be storing things like images that the User does not want to lose."
Of course, for this purpose it is also possible to create a non-app-specific folder.
"We (including Taifun) endeavour to provide a solution that does not require an extension whenever we can, for good reasons: ..."
And again: of course. But in this case there is no alternative.
"Finally you are mocking the App Inventor code compared to the Extension, in terms of what?"
It's far from me to mock something. I'm just showing the only (and for the user simpliest) way to create an app-specific folder.
But, if you did not know it's about an app-specific folder, why do you intervene?