I'm sure it's great, it's just that the rest of the excellent FOSS apps don't have any advertising of any sort. You can support them with donations and such, which I would definitely recommend. I'm using Memmy for iOS.

Also, Material design is cool, but nothing special imo. If anything it just makes it easier to design a nice app, so not sure why I need to pay to remove ads when there are hella free beautiful alternatives.

I'm in no way saying that people can't choose a freemium style app, I just personally don't see the value. Maybe I'll try it out on my dev android phone at home later and see if there's something I'm missing.