Agreed - I wouldn't trim tips either as it's go too much against the grain - I must say there are a lot of flies on display on the web with far too crisp an edge for me to believe they are natural - even at screen resolution you can see there's no natural tapering off of the fibres.
As far as selecting materials - it's damned hard to find many suppliers with Swan - let alone ones within sensible driving distance to go and check out , and that's despite being close to 2 large suppliers - John Norris in Penrith, Cumbria and McHardy's in Carlisle (very good), Cumbria (and alot of packages are sealed nowadays - wish I was a lad again working in a fishiung shop when I had the pick of the bales of capes I used to grade!).
Whilst in the subject of feathers I've just discovered (pretty much by accident) whilst dyeing up some Indian Crow and Toucan substitute that if you double dye a white duck feather (in my case the left over small white shoulder feathers from a Widgeon skin) you can get a really good natural result by...
Well basically by making a pig's ear of degreasing 1st time round, meaning that the colour only takes on the tips of the naturally very oilly feathers, then doing it properly.
The finished result with the toucan using red (which only tinted the tips pink) followed by fluorescent yellow layed on heavy (so it came out rich golden yellow, but with the added glow of the fluroescence) - resulting in a feather with very natural orangy yellow tips fading sharply toward soft yellow at the very base. Similarly the Indian crow - using fluorescent scarlet has a fine soft orangy red base going to briliant red at the tip - cock up or not they do look the business!
Anyway I hear my vice complaining it's being neglected!... All the best
Dave