My company ordered a 0.4mm ObXidian nozzle for our Prusa Mk4 printer. We ordered it because someone wanted to print something with abrasive carbon-fiber-reinforced filament.
It's mounted now and It's the same diameter as the stock nozzle we've been using so far. Since I had to run a print and the bgcode file was made for 0.4mm, I just ran the print with plain old PLA.
And... wow! The difference in quality is staggering. Particularly on vertical walls: they're so smooth and shiny, it's incredible. And the top surfaces are so much nicer and smoother than with the regular nozzle. I printed that particular print several times before and while it wasn't bad, it's never been that good.
I didn't realize the nozzle impacted the quality of the print that much.
I have prints of (almost) the same part here, printed with the regular nozzle at the same speed and layer height. Unfortunately, they were printed with Galaxy Black PLA, and that makes it really hard to see the finish. But here's the best I could take:
Also, the feel is quite different, but that's difficult to convey in a picture.
I'll make proper test-prints later this week. Right now I'm out of the office for Christmas.