It costs some money to continue using it/unlock all features, but that’s a one time fee (assuming that it hasn’t changed).
I can’t use it anymore as IT has disabled all support for 3rd party mail apps. Was the best exchange mail app I ever found (it actually supports the categories using which I’ve organised my mail).
I (and my colleagues on iOS) have no choice but to use outlook mobile as the Apple mail app and everything else is blocked due to GDPR.