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Usually we switch from Github URLs to the project's home page. But in this case there doesn't see to be any information, just a screenshot and links to download/install. HN readers tend to want more information than that.
You can have both. Why people will pay for the app when you can download it for free ? We will see it as a donation. I always start by using FLOSS and if I stick with the software for more than one year I send a donation. Having the app on a store is a way to achieve that. Thank you for choosing to open source the application it matters a lot for some of us.