I don't even know which currency that price is in (Malaysia?), but I bet a Nikon spare battery would have been cheaper. You don't need a dummy battery on the Z6ii, Z7ii, Z9, Z5 or ZFC they can be powered directly by USB C not just charged. e.g. ...
Now, if you remember my previous share on pixel pitches, a Z8’s pixel pitch is actually identical to that of the Zfc. So, if you are sensible, why even bother to operate full frame glasses on a heavier full-frame body, when you can get away with the same at a cheaper price ...