Looks nice but being an Electron-based app is a huge dealbreaker for me.

I imagine it's for Anki users and Anki already embeds a HTML engine (for the cards).

I don't think the main objection that people have to Electron is that it includes HTML rendering functionality. A proper desktop application that includes an HTML renderer for content formatting is a very different thing from a framework that implements an application entirely as an encapsulated webapp.