My first review of a pen, offered with the caveat that I am a definite non-expert and feel a bit of a n00b, loosely following TNS' schema. Images are links to much bigger (and heavier) files. Please excuse the fact that I'm not a product photographer. I was too lazy to dig out the tripod, and I really should buy a light tent...
Conway Stewart apparently make all their pens as they are ordered. I ordered mine through The Writing Desk, and it was in my hands pretty much two weeks later (I'm told the normal lead is about a week). The pen came in a monstrous box that is quite classy but really unnecessary. Over-packaging really does bug me.
This is the pen I had been lusting after since shortly after I discovered the world of fountain pens. I finally got to acquire it when I had a little bit of money as a birthday gift and my parents offered to make up the difference as a Christmas gift to me. It is the most expensive pen I have, currently.

Appearance, Design & Finish. The pen is a flat-topped design, in resin of the pattern Conway Stewart calls White Whirl. In person it is a lively material with some sparkle hiding in the blue. It catches the light very nicely, and as usual the photos really don't show it at its best. The top of the cap and the blind cap are black.
The ball-ended clip is gold-coloured (I presume plate, I guess I'll find out when it brasses) and the cap-band is hallmarked 18ct gold. Fit and finish look grand to me, and I do have a tendency to notice imperfections. The whirl pattern in the resin is presumably unique. I wasn't immediately taken with how my example looks, but it has grown on me greatly.

It's not a heavy pen at all, very comfortable to hold. I like the balance unposted. I have yet to find a pen I like posted, which is fine as I never post a cap.
Nib Design & Performance. The nib is a nice big, yellow-coloured 18ct Fine Italic (marked IF) with the Conway Stewart logo engraved. Line width is a little bit narrower than the 0.9-cursive side of my Binder Italifine. It is much smoother than the cursive nib, much more like a stub. I might choose it over Stipula's 0.9 stub, but it's a close-run thing. There's a bit of spring to it, and it's very pleasant to write with. Most of my pens have fine or extra-fine nibs; this point is fine enough and smooth enough that I can use it without much extra attention at all. I'm enjoying the little bit of definition the stub gives to my scrawl.

When I first got this pen, I was having serious problems with the flow (which I posted about round here). I was only getting a paragraph or two before it dried up, and a shake would let it run for another paragraph or two. And within a couple of days of filling a shake did no good at all, even though it was well full of ink. I sent it off to Conway Stewart to be looked at, and it came back four weeks later (one day's transit each way) in a plastic tube in a padded enevelope (no paperwork, which surprised me, not even a compliments slip). I don't know if the problem was solved at that point, as they had replaced the IF nib with an unexpected M nib, so it went back in the post the very next day. Three and a half weeks later (again, one day each way) it was back with an IF point again and the flow problems seemingly solved. We got there in the end
Now it lays down a nice even, slightly wet flow. I likey. The remaining slight issue is that it can be a little bit of a hard-starter at times. Not seriously, just enough to notice; completely liveable-with, but still just that little bit shy of being perfect.
Filling System. The pen is a button-filler, holding a fair amount of ink - certainly more than a converter-full. It's operated by a small, gold-coloured button hidden behind the blind cap.

My first impression of the mechanism wasn't that great. I found it tricky to operate, mainly because the button is really quite small (more so than I expected) and was taking rather a lot of pressure to operate. However, when I sent the pen in to CS to have the flow/nib looked at I included a note mentioning how awkward I was finding it, and when the pen came back the mechanism was much easier to operate. I don't know if it was faulty or if they just slackened it off a bit to accommodate my feebleness
The options for the Duro are button-fill or cartridge/converter. If I was buying it over I suspect I would go for the c/c (sorry), for two main reasons - the slight fiddliness of the button-filler, and the fact that I change ink colours more often than is good for me and flushing a sac like this just isn't as quick and easy as with a piston or a converter. But I went with the button because I saw it as the more 'classical' option, I guess, especially for my first really expensive (especially by my standards) FP.
Cost/Value. There's no getting away from the fact that this is an expensive pen. The Writing Desk have it listed now at GBP235, which to me is a fairly large chunk of cash to spend on a pen. But here we are at FPN, where we find that there's much more expensive out there, too! I have had issues with it, and some time spent on this forum will show you that I'm not the only one. I went ahead and ordered it in the belief (hope?) that Conway Stewart customer service (CS CS, heh) would be up to the task of putting any problems right, and they have done so - after a couple of goes around.
But is it worth what I paid for it? Depends how you measure... It's a pen I've had my eye on for ages, and it's a pleasure to write with. Costs a heck of a lot more than a biro, but writing with it is a heck of a greater pleasure, too.
Conclusion. Now that I've got it working right, I like this pen a lot. If you want one, I would perhaps recommend trying to find it for less than I paid.