Was said that stand up collar tunic were many much uncomfortable then open collar tunic.
And now...this is the future?
I think the current "mandarin" collar is a rather different animal, (I'll go as far as to say more primitive one in cutting terms)than the classic "Prussian" stand collar of old. The resemblace in this case is mostly passing.
Where the Prussian collar proper is highly worked into shape with the iron and very structured, this mandarin collar has very little (almost no) real shape to it, being practically a flat rectangular band with a strip of velcro on it encouraging a vaugness of shape and fit. Not so much an issue in something to be worn under kevlar, but more so if you're aiming for elegance, something the old style Prussian collar often did have going for it.
I think the US army was right to dub their new collar "mandarin" as it would seem to take its structural ques from tradional Eastern robe-like dress details.
It should be said that a more tailor-made "Prussian" collar need not be unfomfortable at all provided it is made in harmony with the client's psoture (how the head is held in particular) and leave just a touch of gap, preferrably right at the CF while the edges still meet. It is a great place to showcase precision tailoring.