Feature-wise, it's exactly the same app.
When you get it from the Microsoft Store, you download and update the app through the Microsoft Store.
When you get it from Gumroad, you download and update the app through my web server (that's the main reason why it's more expensive, because there's more costs on my side).
I would recommend to get it from the Microsoft Store. The Gumroad option mainly exists for users who don't want to use the Microsoft Store or cannot use the Microsoft Store (e.g. on a company PC where it is blocked)