Not sure about how "zero knowledge" figures into this; is the app merely E2EE? In which case, it's no different from Evernote?

And there is no open source server component, so you can't host this yourself. And say what you will about Evernote, I trust them to stick around way more than another random notes startup thing.

p.s. not to get too political but it seems like the founder is expressing some problematic views on his twitter account (https://twitter.com/thecodrr). Problematic as in, he's this close to being an outspoken supporter of terrorism and radical Islam.