Hey Tom @TMToronto , hey Atroz, hey all,
I found it rather disappointing that when they finally released something new now from the Z assembly department, after a long time, in principle they changed nothing. Still you have only one single linear bearing on a rail, just one size bigger. If at least they had two bearings per rail now, like on X and Y axis.
One thing you get now is four possible heights to attach the assembly to the X gantry, instead of three on the old Z assembly. Does this allow you to have your spindle mount point lower, for the case that you want to work on workpieces of low height? I don’t know.
Atroz, I can confirm a clamping zone and also a minimum clamping surface area on my Mechatron spindle. Will report exact numbers when I find the time. It’s mainly because you must not clamp in the area of the bearings, so it’s a little higher.
At the other end, the further away from milling bit you clamp, the more you increase the leverage force (see 5"ish on trim router) and the risk of chattering on high workloads. That’s why usual Z assemblies on CNC machines do look rather different than the one on Onefinity.
Still no 43 mm mount 
Unfortunately, while many new things just were released, still no 43 mm mount for serious professional milling motors like AMB (former Kress), Suhner, Mafell. In my opinion they still miss something very important . Unlike the Makita trim router, these milling motors are allowed for use in a CNC. And like the Makita trim router, they just need a normal household socket, no VFD, no custom wiring. And some models even have a speed control interface for control by CNC Controller.
By the way, I found this Z slider thread interesting the other day.