There is no comparison between the SJ and the Robur or grinders with Robur-like burrs. And I don't care what the Titan grinder thread says.
I've been doing home espresso on a SJ for years. Great espresso! I learned with the SJ and I loved it. I never thought I would think otherwise. Then I got the HG one (which uses Robur burrs). Since I got that new grinder, I have touched the SJ exactly three times. Then I gave up. Aside from the deeper and more differentiated flavor profile, the Robur burrs offer greater repeatability and consistency. Once in a while I had those god shots with the Super Jolly. But then there were plenty that were "off." Not "off" in the sense of "undrinkable" but just not performing their best. I don't have those god shots all the time with my HG one but they're certainly more frequently. But then, the god shot includes another whole range of variables unrelated to the grinder.
And, I agree that the SJ is a commercial machine which should hold up fine if you use it for no more than 30 minutes out of an hour (so that the motor has time to cool down). Overheating the motor windings is the only real issue I'd see with a SJ in a super busy cafe environment. The SJ, however, WILL deliver in a coffee shop. 99% of your average coffee drinkers will never know the difference between it and a Robur, anyway. This is not to sound supercilious but it is, sadly, the truth.
The SJ is still a very capable grinder. But there are better grinders. As regards MK, I cannot chime in as I don't know much about them taste-wise. I can only imagine they're top-notch.