It's good enough to work, but that's pretty much all you'll get. In many aspects each monitor isn't treated separately by the DE. For example you only have one task bar and each screen gets an exact copy of it. Any minimized window will appear on all the task bars on all your screens no matter what screen that window was from. Right there it's a big turnoff for me. I don't remember the details but just getting a different desktop background for each screen needed a workaround solution as well. They clearly didn't allocate any resources for the multiple display user experience. And now that I've gotten a taste of the insane customizability of KDE Plasma I don't think I'll be able to go back. 6.2 added a layer of polish to the experience that made it perfect for my uses. Which is a shame because Mint was pretty solid otherwise.

I haven't tried xfce and mate on a multi display setup so I don't know. But these seemed to be simpler, being made to be lightweight for less powerful setups so I wouldn't expect them to be as advanced as Plasma for that.