I have had a Model 1 Raspberry Pi for a long time and I never used it. @smilem found a dithering flag, so I was excited to finally get around to taking a look at it.
This old board with a single-core 700 MHz ARM CPU and 512 megs of RAM is about equivalent to a Pentium II 300 CPU, though the Videocore IV GPU is basically equivalent to the first Xbox so it can do hardware acceleration of h.264 video.
Bullseye Desktop - Very slow, you can type faster than the letters appear on the screen. Defaults to KMS (kernel modesetting) which I didn't like as it's shimmery a bit. 5.15 kernel.
Buster Desktop - More acceptable speed, 5.10 kernel. Still too slow. 3 options are available for video driver here (you can switch between them in advanced settings in raspi-config), legacy, fkms (fake KMS) and kms. fkms and legacy are ok but not better than the Intel driver config I have on Windows. I tried the undocumented dithering flag with various combos on the legacy driver and the fkms driver, I didn't really see any difference, but I also wasn't testing with gradients or anything. I just wanted to see if the wallpaper would shimmer differently. No one with a Model 1 is going to get any value out of the desktop experience due to speed, and the console, what's the point if you're not running a server? The notes say that older versions of Chromium were hardware accelerated, but I didn't see that still being the case checking in chrome://gpu, but this thing doesn't have the resources to handle the modern web anyway.
FreeBSD - Ultra bare-bones. Dumps you into a console prompt. Console rendering didn't look as good as in Linux, but I also didn't spend any time in it to configure it or install X or anything. Doesn't really load or start anything, so it is very light on resources (good for server and the console painting doesn't matter because you'd normally be using SSH anyway from your regular machine).
RISC OS - This one was REALLY nostalgic and I found it charming, the GUI from the Acorn from 1987. It resembles Windows 3.1. It is really fast! The GUI flies. I wasn't able to set my monitor's native resolution. It has a browser, but I didn't try it and it wouldn't have been worth it anyway, because it's from years ago. It was comfortable enough to use, but let's be realistic.. is anyone today going to be using RISC OS for anything today?
So a mixed bag.. it was good to finally get around to taking a look at it, but I wouldn't recommend something this old to anyone at all due to resource/speed constraints. The Pi 4 has 4 cores, more ram and videocore VI graphics, no idea what it would look like on my monitor but would be a much better desktop experience compared to the first one that's for sure.
So, Pi 1, nice toy, good only for servers and projects using the GPIO pins.. if you need to make a garage door opener or something, this is what you need. The Pi's real strength is the GPIO pins.. when it came out, it was rare to find the ability to interface with something like you used to be able to do with parallel port pins. Arduinos were around but they aren't something you'd be running an OS on, they are much more basic so the Pi was basically the first widely-available unit that could be used by creators.
No eyestrain panacea here with the model 1, but it was fun to play with.