Most of the times the paid version is free when the new update comes out. Then the new version will cost something and the older one doesn't and the updates come out at around the 20th of every month so it will probably be free pretty soon.
Great Game, i have a question though. I bought the 0.4 version, will my purchase work for the next updates aswell? Don't get me wrong the update is quite nice but i think paying 10$ is a bit expensive for such a small update.
