I actually think this is a nice app but when I first installed it I was incapable of logging in, as the app only allows ID/password login, not Google or Facebook authentication like the site. I had not configured an ID and password so I was S.O.L. until I got into the site from my laptop (the mobile site also hides the account settings page where this is configured) and created my native Flowdock credentials.
Maybe this does not affect many users but its a glaring deficit to not support 2/3 of your supported use cases in the mobile app.
Joel in Brooklyn about Flowdock