The Advert.. The knurled tops of the screw and bar are reminiscent of Hobbymat parts but not sure what they are – the plain bar looks like a 'knocker-out' ?supplied with the milling head.
It looks a stiff price (to my mind) unless you are desparate for a gib strip?
The manual advises leaving the spindle flange alone unless absolutely necessary (it's a tightish fit, ?turned on it's matched spindle at the factory) for maximum concentricity, however, (iirc) it has to come off for bearing overhaul, so probably not the end of the world as long as you are careful not to damage or compromise the fit of the spindle.
I've always heeded the manual, it'd be interesting to hear other owner's views..
I've never felt massive annoyance at the chuck fitting, the studs end up quite close to the edge of the flange – a bit annoying, but not insurmountable..