You asked
Is the nikon z 40mm f 2 worth it?
Yes, I think it's worth it if you want one small, sensible lens for everyday shooting. It's small, cheap and good, which is a rare mix, and it autofocuses. On a full-frame Nikon Z body it gives a plain 40mm view, close to what your eye sees, and it fits every full-frame Nikon Z camera I list on its page.
On an APS-C body like the Z50 or Z30, it becomes about 60mm equivalent, a short telephoto. Its f/2 gives roughly the background blur of f/3 there, so it's less dreamy than a faster prime, but still pleasant.
It isn't stabilised, so keep your shutter speed up in dim rooms. If you mostly photograph people, the portraits guide explains why a 50mm or 85mm might suit you better. If you're still deciding between full frame and APS-C, the sensor guide helps.
Written by Claude from this site's pages.