Using rsync for syncing files from the one Linux device to another is very slow. And I imagine it's not the best option for doing so, because I don't care about copying over only the bits that have changed because most of the time the changes are file adds/removes. (i.e. if a file has changed, I don't care that the whole file needs to be copied over)

So do I have any other options for syncing? Somewhere I read that maybe the cp command with the -u flag could achieve the same result but with faster transfer speeds - is this the case? (The only problem though is that the device I'm transferring from has an old version of cp that has no -u option, but I'm guessing could mount both devices from my laptop which does have the -u option in cp...) But I also read that if I use the -u and -r options together, it defeats the purpose because if a file has changed the whole directory's timestamp has changed and therefore everything gets copied...

Basically I'm wondering what options I have that are faster than using rsync for syncing?

Copying only the bits that have changed speeds-up the copy, it doesn't slow it down. You have the option in rsync to ignore timestamps or file size checks as well.