Yep, this is a good option for reducing file size at the expense of compatibility and CPU time. Every time OP downloads a file they’ll then have to reencode the file, which can take significant time, depending on the CPU of their NAS box, the file size, etc. It’s also worth noting that reencodes are lossy, so some amount of quality will be lost (although the quality difference may be imperceptible).

If disk space is the only variable we’re optimizing for, then you’re 100% correct, but I think it’s worth calling out that this definitely isn’t without tradeoffs.

It might also be worth considering how they’re consuming this media. If the client isn’t capable of playing back h265 then this will need to be transcoded again to play it back. Many media servers (like Plex) handle this automatically, but it’s definitely worth testing this out with your setup on a couple of files before doing this on your whole media collection.

In general, the stability of custom roms and random bugs you encounter may be more than with officially supported operating systems. It might be totally fine, but if you’re the only person who has encountered a random bug and no community dev is interested in fixing it right now, it might stick around for a while.

If it’s your only device and you need it to work, I might recommend trying it out on a secondary device first to make sure it works for what you need.

Philosophically I agree and am aligned with open source and free apps, but the reality is I don’t have the time or patience at this time in my life to deal with that kind of thing. Your calculus might be different though.