Thanks!
Andrew, it actually wasn't great. I didn't have as much control over line thickness unless I consciously turned the quill to use the edge for a hairline. Earlier this week, when I had cut the nib wider, the flow was actually quite dry, so the line thickness behaved well, but I wanted to use a smaller x-height, and after re-trimming the edge I lost crispness. It's quite possible that as I get better at cutting the quill, or if I do things like season it properly in an oven, rather than leaving it in a drawer for eight months, I'll find I can make the line variation obey my will, but for now it's mostly trial and error, and most of the time when I try to re-trim the quill I get splayed tines or an off-center split. Simply having a tip that mostly works is a triumph.
Randy, I can't compare a seagull quill to any others, as it's the only quill I've ever used. As for the reservoir, it certainly seems like a great idea, but in fact it was a necessity. Without it, the ink all just flooded off in a big glop. I don't think the old masters had mass-produced William-Mitchell reservoirs to stick on their nibs, so clearly they were doing something that I'm not doing. I'd really like to be able to mimic that, but for now I think writing with a quill will be a fun novelty, rather than a technique I'd turn to if I'm creating something serious.