Fun fact: the latest version of this software uses SwiftKey under the hood - http://swiftkey.com/en/blog/swiftkey-reveals-role-professor-... (Disclaimer: I used to work for SwiftKey)
It begs the question though, why isn't there a proper SwiftKey keyboard for Windows? The OSK on 8.1 is awful compared to SwiftKey on Android. The Windows 10 is a improvement, but I'd still pay for a better one.