It makes a difference, but how much of a difference and do you or I notice and value the difference?
For someone like Frank, who ran the comparisions, it makes enough of a difference. But he’s got a cafe, imports espresso machines/grinders and has a lot of tasting/cupping experience. With his finely tuned taste buds, James Hoffman may have RPM preferences too.
Not for me, not at this point anyhow.
I seem to get pretty good espresso from 500 - 1400pm, depending on the grinder. The Honne was 500rpm and the Moca around the 1200 mark. Both yummy.
And like someone has posted here, there are other variable to tweak such as grind size, and for those with the machine features, variable pressure, temperature. Not to mention cleaning under the shower screen and buying quality beans.
That said, I am finding that there is a spectrum. For example, things that don’t make a difference with a dark roasted bean used in milk drinks, make a massive difference in a light roast filter drink. WDT, bean freshness, bitterness and more. So maybe RPM is one of those things that makes zero discernable difference in espresso/dark/milk but a sigificant differnce in light/filter?