It's just a MVP... version 0.01 of their vision. The fact that they have paying users who use them daily is a very, very good signal - that's a hard thing to do! It's so much easier to add additional features to that group of users later.
The V in MVP stands for viable. Things that aren’t viable aren’t MVPs they are steps getting to an MVP. Part of the value of testing stuff is to check and see if what I think is an MVP is, actually is. When it clearly isn’t, if I call it an MVP then I’m either insane or a marketing person.
Prototypes are perfectly cool as long as expectations are met. Of course, charging $10 for a prototype doesn’t frequently work
I see so many negative comments and can't help but think of this (first comment on DropBox's HN launch): https://news.ycombinator.com/item?id=8863