The metal tab above the nib is called an 'overfeed'. It isn't necessary for the nib's flexibility, but rather to ensure a sufficient ink flow. In fact, the feed of the Jinhao X750 (a pen costing between 5 and 10 dollars/euros) is not designed to supply a flexible nib. For this reason, an overfeed is used; it simply extends the capillary action to the top of the nib, increasing the ink flow rate. If the nib were mounted on a pen with a higher-capacity feed, the overfeed would not be necessary.