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If you are concerned about the security of the app, you should try bug bounty programs where people search for bugs in your app. I recommend www.bugcrowd.com or www.hackerone.com. You can choose to give reward for bugs or not. I think it's important for an app like this to be secure because it holds very confidential informations!

Do you have development skills?

I'm actually a Hacker by trade, I just decided to switch to design recently so I agree with you,security is very important.

Same for me, I'm more in the security field! Maybe you can find some developers here!