A bit of unsolicited advice -

* Focus on Windows users. Windows desktop share is 10x that of Mac and nowadays Windows users pay almost as willingly as Mac ones.

* Charge several times more.

* Redo the website. In particular get rid of 3D slant and on-hover animations, put larger high-res screenshots, explain each of them well (and not in gray on gray text), put up "Windows / Mac / Linux" in bold friendly and highly-visible letters. Better yet have separate Download buttons for each. Add version and last release date, next to the Download button. Have at-a-glance summary of features closer to the top of the page. Ditto for pricing and trialing details. Ideally, adjust windows chrome in the screenshots based on the web client's OS, i.e. show Windows screenshots to Windows visitors, Mac ones - to those coming from Macs, etc. The last thing you want to show Mac screenshots to Windows people, because it implies that the Windows version was an afterthought.

All in all, the site gives an amateurish/hobby project vibe, and the $5 price cements the impression. If you are to spruce things up a bit, you can potentially live off this app. At the very least and with not much of an effort you can double/triple what you make off it.

Thank you for all the suggestions! I like them and will try to implement at least a few in the coming year (I end up spending more time towards other exciting projects like writing a sci-fi novel and DIY remodeling my house).

Woudln't OP be able to tell what the platform split is just based on his internal download metrics?

Did you bother to look at the source code? It's Electron-based, so the effort for supporting more than one OS isn't very high.