Seems like a wonderful product, but I'm with the others: I probably won't be using it if you need my personal information first. It's a dark pattern (not that I'm accusing you of being malicious) to force people into disclosing anything to use your app, so I'd recommend adding a simple feature like bookmarks that signed-in users can get as a bonus. Otherwise, I see a lot of red flags as a developer when someone is so upfront about needing my email.
Regardless, keep up the good work!