@DavecUK can confirm. I think the existing burrs carrier is optimised for Mazzer 151B and we can’t swap the burrs as easily as we would like to. I also believe SSP HU will fit the existing carrier.
IMO, offering different burrs choices for espresso likely require respective unique carrier designs, optimising tight tolerance and perhaps tweak the design a little for each of them. This doesn’t end here. The motor may need to be customised or optimised further for each choices.
I don’t think there is an efficient one-size fits all solutions here, knowing Niche doesn’t do a sub-optimal job.
However, there is a gap in the market in this price bracket. I do think Niche may want to look at the possibility of mounting different burrs choices at sales, and after-sales. Sure, it will cost more.
Irrespective of what people think, offering dual burrs is innovative and is still a great idea. We are just lazy that most of us can’t be bothered to use it and we don’t appreciate it enough.