Latest betas include Apple Music/Spotify integration, Speed control, and brings back the ability to put your videos anywhere (including an external drive!) on Monterey.
It's open source too, according to the description, it streams and doesn't cache videos and apparently it handles 4K HDR. If data usage is a concern to you, be aware that some videos are close to 1 GB.
I use this one on my TV, and it's great, highly recommend.
If bandwidth is a concern, you can also point it towards a local JSON file with whatever URLs you want, so you can mirror the screensavers locally and then stream them from there.
Part of the reason these are so captivating is that they are slowed down instead of real time. This gives them an other-worldly quality where you can see extreme detail but in a different motion than you would normally see it.
Many of the cityscape ones I don't believe are slowed down, at least the ones I have seen. If you watch the movement of traffic it appears to be moving at normal speeds. Even the orbital ones appear to be real-time.
The otherworldliness of the video seems to come more from the smoothness of the motion and the uncommon perspective. Because many of the scenes are captured with drones instead of helicopters or airplanes they have a literal bird's perspective in terms of velocity and altitude.
It's been an ongoing debate I've had with some Aerial users, but I agree with you. Most if not all are real time or barely slowed down (latest beta I've put a slider to speed a video up/down partly to try and settle this).
They definitely are massively stabilised though and Apple used to update videos from time to time, tweaking stabilization, colors or sometimes length and pushing new versions. They haven't done that in a long while though.
Some seem shot from fairly high altitude and may use planes instead, and at least for some videos, I've heard they used 3rd parties to shoot them.
The other reason is that you have to have biggest-company-in-the-world-sized connections (and pocketbook) to get permission to run a 120fps 8k drone over an active LAX.
I'm sure for the right opportunity they'd work with anybody. I suspect it's not a matter of connections, but rather, "We'll put a gorgeous shot of your facility on millions of TVs worldwide" is a slam-dunk pitch.
https://youtu.be/lbj9kihTwcc