I thought Apple barred iMessages from being sent/retrieved outside of the specific iMessage app? How did you dodge that?
How in the world did you get iMessage to work on Android and Windows? This was a tough one to figure out! Beeper has two ways of enabling Android, Windows and Linux users to use iMessage: we send each user a Jailbroken iPhone with the Beeper app installed which bridges to iMessage, or if they have a Mac that is always connected to the internet, they can install the Beeper Mac app which acts as a bridge.
Still, it seems like they didn't really dodge anything at all. It's the same gripe I had with Signal: if I have to switch between iMessage and Signal, then I'll never be able to sell Signal to my family.