I’m reticent to say anything here because of the massive popularity of these burrs.
When burrs were designed, it was for grinders with hoppers, not single dose grinders…this gave the basic burr design. The geometry of burrs, the crush zone area and angle, as well as burr speed all contribute to the beans feeding the burrs properly. In a single dose grinder this is compromised.
Consideration has to be made for the modern practice of single dosing on high-end grinders, especially flat burrs. in the Niche Zero, there was the flow control disk, which helped the conicals maintain a uniform grind rate…so much so that if you plit the grinds into 1st and second halves and then put both 1sts and both 2nds together and made individual shots, the pour times were the same.
In flat burr grinders this is much more difficult to achieve, and the burrs have to be a lot closer together to grind than they are when a hopper is used. Sometimes so much so that they can touch when the beans have passed through the burrs and is often the reason for marks on the burrs. There are a set of challenges to overcome, and alignment is more critical when single dosing. Having a low size variation is difficult as the dose is ground to completion. These challenges can be overcome/mitigated by various techniques.
Are HU SSP burrs actually better when single dosing? The honest answer…I don’t know, my experience has been that they are challenging to work with.