I broadly agree with his opinion about the stock Duo 151B Mazzer burrs versus the Konys in the Zero although I do think the latter offer more body. Taste wise, I don’t experience much of a difference, if any.
For me, the Duo stock espresso burrs offer a mainstream, traditional, smooth, inoffensive espresso that fails to excite. Again, just me, but there are much more intersting espresso burrs out there.
Other more interesting options for me, including the humble and inexpensive Varia Hypernova series (three of them), the DF 83mm flat and more.
The Duo’s appeal is restricted by Niche’s decision not to condone the use of different burrs sets. Even using the sublime Mazzer k151H espresso burrs will void your warranty. In the 83mm flat range, the DF Espresso, Gorilla Gear, SSP Espresso (HU) are all burrs I’d have over the stock Duo espresso burrs.
And by opting for those burrs (151B) and not embacing burr swapping like so many other companies (Timemore, DF, Gevi, Zerno and so many more) and insisting that only the stock burrs are used for espresso, Niche have limited their market appeal. (DF must think that Niche’s inflexibility is a dream come true.)
FWIW, for me the Duo is a completely superb grinder. But Niche’s refusal to allow burr swapping, makes it like a Formula One car that has a controller limiting the speed to 100kph. All the other cars/grinders can perform at a higher level, not because they are better grinders, but because they allow for better (in my opion) burrs.
If Niche would only permit burr swapping, then for espresso it would produce world equalling performance in the cup and it would likely outperform everything else in the same budget bracket for retention, durability (not tested but likely), workflow, ease of deep cleaning and overall value for money. I’ve tried twice to convince Niche to change their policy but unfortunately to no avail. Crossing fingers that they will relent eventually.
God forbid, but if I had to have only one espresso grinder on my bench, it would be the Duo. But not with the stock burrs.