I used a Nismo knob in my NB, same thread pattern, sits a bit lower and I loved all the dumb looks I got
The guy I sold the car to didnt cars for it so that nismo knob now resides in my 350z.
Not a weighted knob but the miata transmission is fantastic and doesn't need any additional weight, i'd worry more about adding weight and wearing out the turret bushings quicker. Weighted knobs are great for fwd cars where linkage or cables makes the stock shifter feel vague.