I found out from fountainpennetwork.com that xfountainpens.com is selling the German made Knox K35 nibs that fits the Jinhao X750 and Noodler's AHAB pen and are very smooth so I ordered a set of 3 for US$18 and that came with a 'M', a 'XF' and a 'F' nibs. Here I fit the 'F' nib on the X750 and it's much smoother than the original (while the original was already very smooth).
No, I don't think that's real gold at US$6 a piece.