I was thinking about my pens and I got to wondering about feeds and how different they all look, and how their shapes might influence performance. My Lamy Safari has a very streamlined feed, sloping up parabolically against the nib. The Vanishing Point has a tiny feed fitted to its tiny nib, Pelikans and Auroras have stout feeds that I find attractive, the Pilot Custom 823 has a kind of combination, with a very Lamy Safari looking portion with a hole near the nib's tip broadening into a flat section with fins near the section. Sailor feeds have an area which seems to be under the breather hole where a tiny cube would fit. Some feeds fill the whole underside of the nib, and others leave plenty of space in every direction.
Is there a functional difference that leads manufacturers to design their feeds with so many shapes, or is it mostly aesthetic? They all do their job despite coming in so many different shapes and sizes. Are there flow differences between shapes; is it a matter of designing a feed that goes along with the nib's geometry; a feed that goes along with the design of the pen? Is there a particular design that's well suited to tolerating differences in pressure, temperature, and humidity? Ebonite seems to be very respected as a feed material - would a feed made of ebonite be preferred over a plastic feed of the same shape?