I keep nearly buying a multi-material upgrade, and I keep talking myself out of it, so this is me writing down why before I forget and nearly buy one again.
The appeal is obvious. Two colours, or a soluble support material, or a flexible part fused to a rigid one, all in a single print with no babysitting a manual filament swap at layer 40. When it works it's genuinely lovely, and the soluble-support trick in particular solves geometry that's a misery to print any other way.
The cost is also obvious once you actually look. A single-nozzle multi-material setup spends ages purging the old colour out before laying down the new one, and that purge has to go somewhere: a wipe tower, or a purge bucket, or just sad little blobs. On a print with frequent colour changes you can easily throw away more filament into the tower than ends up in the part. It's slow, too, because every change is a purge and a prime, and a four-colour print can spend most of its wall-clock time just cleaning the nozzle.
So for me the answer is: worth it for soluble supports, worth it for the occasional showpiece, not worth it for everyday printing where I'm making functional single-colour parts and the swaps would just be vanity. I'll keep the manual pause-and-swap in my back pocket for the rare two-tone job, and leave the proper multi-material rig on the wishlist for one more year. Probably.