It’s pretty slick to be honest, way smoother than Ubuntu on the same old machine. It does largely feel like Android though, and it’s Google all over.

Not sure why someone would want to try it. It's basically just Chrome OS but more limited, https://support.google.com/chromeosflex/answer/11542901?hl=en

Some of these are really severe - no CD/DVD support? Really?

Also more concerning, is that Chrome OS Flex might become unsupported soon, as per https://www.zdnet.com/article/google-might-abandon-chromeos-flex-next-heres-why/

For the technically minded trying to keep up to date and secure older hardware, a good GNU/Linux distro seems like the best choice. And it's not so hard to set up a good Kiosk if setting up the older hardware for a less tech minded person, https://oofhours.com/2023/05/02/creating-a-kiosk-with-linux/

That said, although I haven't tried it myself, I found a good story about someone's success with Flex, over at https://www.zdnet.com/article/i-revived-three-ancient-computers-with-chromeos-flex-and-you-can-too/