Personally I never bought into the whole Apple logic of having to syncronize your library with the device. It feels like an overly complicated way to solve a simple problem. I’m mentioning this to give you a perspective on my advice that follows.
Personally I really like devices that work with the standard tools the OS provides, in my case that is Finder. My preferred workflow is: attach PMP, open finder, drag&drop files, disconnect, done.
I also like devices that come little extra stuff.
From that perspective, and after quite a bit of research, I landed on the FIIO X1 mk2 (as mentioned above). Which works well with MacOS, does not rely on weird proprietary protocols.
Of course if you want to drop your complete music library on it that might not work (I think it supports only up to 256Gb for the SD card) and for that synchronizing might indeed be a better option. But maybe it’s more aa matter of how you approach it?
You know… sometimes one gets very fixated on how things should work, and there’s all these things that are so super important about it, just to find out that it wasn’t all that important after all, and it’s mostly a matter of the perspective you have on things. At least that’s what happened to me many times.