I mean, for 10 bucks anything is a decent deal. Those specs are pretty decent for a simple home server. I'm not familiar with HP thin clients, but I assume you can install a Disdro of your choice on it? My big reason to avoid HP is their crap software and warranties, both of which are moot here.
I would say relatively light software like tailscale, pihole and such would be fine. Docker containers might be pushing it, but that depends largely on what containers you want to run, same goes for nginx; by itself the requirements are fairly low, it depends on what you want to run on it.
Jellyfin might be a stretch, and as you alluded to, real-time transcoding is probably out. It strongly depends on the decoding capabilities of that chip and wether it does hardware decoding or if it all happens in software. The latter might be too much for it. If it can handle it though, it might be interesting as a media player hooked up to a TV, rather than acting as a transcoding or DLNA-esque server.
I frequently amaze new colleagues when I show them that deploying an update for our backend application is a sub-second affair. Our pipeline keeps track of what git tag was deployed last, diffs between that tag and the new release, and uploads the files to each of the deployment targets. It takes longer for the pipeline agent to spin up from Cold on a Monday morning, than it does to actually deploy.
The core of the application is just php scripts, and those are either immediately up to date whenever the next call is, or swapped out the next time that component finishes a processing cycle.
Docker containers are nice, but nothing beats the cause of a stack trace being fixed, tested and deployed to the acceptance environment within minutes of it arriving.