Yes, I have an FNF 2-channel ebonite feed in my 743 FA, which improves ink supply considerably. I ordered the feed the same day I ordered the pen.
I haven’t bothered getting one for my 912 FA; when I ordered the 743 the 912 ebonite wasn’t then available… apparently it was unusually tricky to perfect. While it’s now available, I don’t use my 912 FA enough to warrant the upgrade.
It’s an interesting area. Some thoughts, for the incredibly few who might possibly care:
Little known, but the stock Pilot feed is made of two parts; there’s an inner section that can be easily modified to increase flow, by just scoring out some more plastic to make for a wider tube. That’s how I’ve improved my 912 for better flex performance.
However, increasing flow isn’t the whole story.
The Pilot stock feed is designed as a one-size-fits-all for all nib styles, and the FA nib is a niche item. So, it’s (presumably) optimised for the standard nibs “constant-flow” nibs, and for manufacturing.
It’s also probably optimised for the short non-continuous strokes of Japanese script, where the tines can hold enough ink to complete each stroke, so continuous variable ink flow needed for continuous flex isn’t really what the stock feed is best at.
As I understand it, those nibs are also ground for a more upright holding angle, used in Japanese script, traditionally with an almost-vertical brush angle. I find my 912 FA writes much better when held more vertically than I’m comfortable with.
Put all of this together and it’s understandable why some western writers – especially those with a lot of continuous stroke cursive and a relatively low pen angle preference – have flow problems with the FA, at least with the standard feed. I suspect this is why they don’t really market the FA much outside Japan… I bet it’d be a customer support nightmare compared to the solid nib variants.
The ability of a static feed (eg. a solid single component rather than a sprung or hinged thing) to keep the right shape for an arbitrary nib deflection is questionable, no matter whether ebonite or ABS. More likely, the wetting factor is what matters;
I do tend to prefer ebonite for flex; while non-CNC ebonite feeds (eg. Noodlers, FPR) are so rudimentary compared to injection-molded and etched ABS, a good ebonite feed does seem to support flex better. However, being cut mainly by hand, it’s a crapshoot; I’ve had as many bad Noodlers feeds as good, and a few that on inspection are defective and will never work properly.
Saying that, I’m also not entirely sure it being ebonite is the big deal… there’s a lot of smoke-and-mirrors around ebonite, wettability, etc.; I think an ABS feed machined with the same precision CNC process, rather than injection-molded and etched, might perform as well as the ebonite. I’d like to try one of FNF’s clear acrylic feeds sometime.
My conclusion is that it’s probably possible to mass-produce a good flex feed in plastic for western script, but being CNC, not at the budget end of the market. A CNC ebonite feed is probably the best option right now, but while the Pilot FA nib (either #10 or #15) is probably the best mass-produced (albeit low-volume) modern flex nib out there, it’s not ideally suited for western flex writing.
Vintage still wins, but not just because it’s “vintage”… more that it was optimised for western script at the time, and used ebonite feed material; any limitations of the feed-cutting process compared to modern CNC or injection-molding is compensated for by a) use of ebonite; b) better skill at nib optimisation; c) economies of scale; d) higher pricing, comparatively; e) possibly (but unlikely) binning strategies.
It’d be interesting to see what a giant like Pilot could do if they properly concentrated on making a premium flex pen for western-style cursive hands, rather than on Japanese writing.