Like Ilkka, I also find NX-Studio quite useful and not too slow on a decently specified machine. Besides, my usual Photo Ninja workflow is at present hampered as it does not support Z9 files. PN can process them, but the outcome is not optimal. Thus NX-Studio comes to the rescue.
What annoys me the most with this software are two things; firstly, how slow it reads files across a local network, and secondly, that the user interface cannot be expanded to multiple monitors /separate windows are not detachable, This makes the UI cramped and hard to read, and even harder to use in a relaxed manner. To be honest PN also shares some of these traits, but as its UI is much simpler the problem is better mitigated.
I would wish Nikon was less eager to make prior Windows versions "obsolete" as seen from the software's point of view. NX-Studio will only run on Windows 10/11 (OK, Macs too I presume but these are of no interest to me). Technically it should run on Windows 7 as well, and a pipe dream is seeing Nikon software run under Linux. Photo Ninja does even though the maker doesn't mention this fact.