I also had a quick look at your privacy policy, and agree with what oarsinsync mentioned. If you could skip asking users for their details, but still allow them access to the tool, you would probably have a lot more users sign up. Before they sign up, you could store their bookmarks locally. Then perhaps later on, you could ask them to sign in to save their bookmarks to the server to be accessed on other devices.
However, this all depends on what way you plan to monetise the app/extensions?
Can I also ask what framework are you using for the mobile app? It isn't React Native by any chance is it? I ask because I'd love to know how you got on with building the app for the App store. I hope to publish iOS & Android apps for DarwinMail[1] in the coming weeks.
Also, it would be absolutely amazing if you built the Chrome extension with React Native and had some tips.
PS: The site is down ATM, probably because of the influx in all the lovely visitors from HN :)