Chrome doesn't support hardware acceleration video decode on Linux at all. There's some unofficial patches for VaAPI support if you want to carry those around, but the Pi 4 also changed decoder support and it's generally all just a messy disaster.

Low-res video can be software decoded fine, but once you start pushing 1080p or 4k it's not going to go well at all.

There's no shortage of chromebooks in the $250-300 range which then also include a display, narrowing the price difference drastically.

Of course there's also used options, which is also a good option for ipads and such that would still be a much better option than this for a non-techy user.

The Rpi 400 looks fun, but it's a tech toy for hobbiest electronics usage or general hackery. Not a generally good computing appliance for the masses.

Still behind an experimental flag, though, isn't it? I don't think https://wiki.archlinux.org/index.php/Firefox#Hardware_video_... really qualifies as something I'd want to send a non-technical person through.

Fun if you're into it, incredibly confusing if you're not. Which also means amazingly ~7 years later this XKCD is still relevant https://xkcd.com/619/