I just downloaded and have been loving this. It loads pretty quickly, navigation is intuitive, and I'll finally stop forgetting that Nebula exists because it'll all be in my one big subscription feed.
Since I'm new to moving over to open source, I want to ask the veterans: is this as incredible as it seems right now, or is there something I'm missing?
Trademarks. Anyone malicious can take your source-available code anyway, but if they infringe on your trademark by calling it "Firefox" or "Newpipe", you are legally in your right to take it down. Trademarks deal with fraud; copyright doesn't.
Iceweasel is a classic example of what happens when free software projects like Firefox seek to defend their trademark. They didn't want to allow Debian to use the Firefox name, as that may cause users to attribute quality problems to Mozilla when Debian is actually responsible because of the patches they had made.
Want to remove an app using the GrayJay name without your permission if it's a registered trademark? Here's a link to report it to Google Play.