Disclaimer: I haven’t read the article

A wise choice in this case. It’s 23 paragraphs that mostly describe standard Thunderbird features (as the author usually does not use email clients) and only one list with three (!) bullet points of new features in Betterbird.

Edit: to save you a click, here’s the list from the article (the actual feature list on the project page is longer):

Some notable features include:

• System Tray Icon (Linux)
• Accent Colors (for folders)
• Multi-line Inbox View (disabled by default)

I hate this “feature” but there is always a way to deactivate it in both the web version and the app: you can change the audio track on the settings of the video (e.g. behind the cog icon on mobile)