Let me explain:
The game is for everyone,
regardless of whether you paid for it or not.
Version 0.6 is currently available for those who pay on that website,
but when it’s released here on Itch.io,
it will contain the exact same content.
In other words, if an update includes a story mode, for example,
both groups will get it.
The only difference is that those who pay get to try it out sooner,
while those who don’t pay have to wait a bit longer.