So far, I've just been exploring the interface, and I'm really excited about it. Thanks, Sam!
When I run the AppImage from the console, I get a long list of warnings about fonts (which don't seem to cause any problems):

[...]
Fontconfig warning: "/usr/share/fontconfig/conf.avail/48-guessfamily.conf", line 172: invalid constant used : ui-serif
Fontconfig warning: "/usr/share/fontconfig/conf.avail/48-guessfamily.conf", line 180: invalid attribute 'xsi:nil'
[...]

In Resources, you can create subfolders within custom folders. I've been wanting this feature for a long time. Visually, the subfolders aren't nested under their parent. They all look like similar bins.
Speaking of bins, I have a question: what are global bins?
The Smart Bins window and how they work are fantastic.

I really like the ability to save and export my custom configuration from Settings --> Preferences. That way, I can load it into new installations without having to access the hidden .bcast5 folder.

I really like how the Deliver tab is organized (with the most important presets right in plain sight). I tried rendering from H.264 to ProRes 444, and everything worked fine. It also seems pretty fast to me, but I need to compare it with CinGG/guicast.

The “View” menu doesn't seem to be working properly (I couldn't turn off the fade), and neither does the “Mask” tool, but I only did some quick tests and need to look into it further.

I'll try it out more thoroughly tomorrow.