Tried a Palette 2s for a few weeks before returning it - even wrote my own Duet 3 plugin for the feedback loop. Tried it with several different printers including a custom built one, and tried it using a variety of extruders and hotheads. Not worth the time or money.
Their support is completely unhelpful (I ended up reverse engineering the octoprint python plugin) and while its pretty piece of hardware, it is largely a very expensive paper weight as another commenter mentioned. Several design flaws make it very frustrating to find the right settings for material combinations since it clogs all the time, forget doing true multimaterial (not just multicolor) printing unless you make a binding layer (TPU) or chose compatible plastics since most stick together worse than PET, and the closed loop feedback mechanism is far from good enough to have even 50% success rate. I managed to get a few decent prints from the contraption but it required babying the 3d printer even more than before. If you have wild humidity or temperature swings (such as when doing a long 10-20 hour print), you can forget about any sort of reliability. Oh and it is slow - best I've gotten on the 2S is 40mm/s (one of the printers I tried it on maxes out at 200-300 mm/s, though few materials can support that speed).
That said, without that closed loop feedback, the method described in the paper simply will not work on nontrivial prints. If I'm understanding it correctly, it's just doing the same thing as the Palette except not in real time.
I know three people who own this, two think it works fine and one thinks it is junk. I have been tempted but haven't wanted to burn up $300 on the off chance it does what I would want.
My original Makerbot Creator 2x has two extruders so you can do two materials, but print failures where one of the filaments stripped were more common than print successes. It was why I didn't bother looking for a dual extruder when I replaced it and ended up with the Prusa MK3S (which basically had everything on it that I would have put into a printer I built myself).
In my experience its absolute junk. There is too much friction throughout the entire systems. So it often slips the filament when extruding or retracting. Leading to clogged nozzles, holes in the filament and other nasty business that take a lot of time to fix. I've rebuild the one I have tree times now but it keeps misbehaving. I can't rely on even 10 tool changes working out. And a big multi-material print often takes hundreds of them.
Its in stark contrast with the Prusa printer itself which I find to be of extremely high quality an easy to use :).
I also have two friends who have the MMU. For one them it always worked perfectly. For the other friend the first one didn't work at all, but once Prusa replaced it with an orange one (they were very explicit about that) it did work a lot better.
If they'd work decently - ask people who have them, i "know" at least two on a 3d printing discord and what they have is basically a pretty expensive paperweight...
I once saw some video about the buffer and the way it is flawed - also don't expect any print speed if you're using it :S
From what I've heard, there is a lot of filament waste still. But the results looks decent.