Not sure it can handle thousands of emails and the UI doesn't look "professional" but there's a lot of good ideas and after a while, I guess it could be a new and effective way to use emails.
Every two other week, someone writes that openGPG is broken. Guess what they want to say is that if you use PGP in certain ways, it's broken (keyservers, addons like enigmail and so on).
But nobody has ever been able to demonstrate that it's broken if you use it correctly. I'll stick with openGPG.