cboody - thanks for your comments, with which I mostly concur - I only differ in that I do see what folk mean who think it has an aspect of a recordery sound. It is indeed “problematical” in the upper 2nd 8ve - Jon actually mentions this in his accompanying sheet of instructions, recommending using xoo xxx for high B if it is needed to sound more softly and clearly - which does in fact work well, but isn’t too handy in fast tunes. It is an accepted and acknowledged (by JS) consequence of the deliberate low register optimisation which is so successful. It’s a trade off - you can’t have a good high end with the same set-up of bore and voicing. Most (actually as opposed to allegedly good!) whistles of any design and intended playing style are more balanced across a 2 8ve range, and consequently can’t have as much bottom. So, it is definitely the instrument, though the player may not yet be getting the best from it.
Even Swayne’s high whistles have this bias, but it is less extreme in a smaller instrument and the full 2 8ves are fully usable. Nonetheless, my high D by him does not go usably well into the 3rd 8ve as many high Ds do - it has to be pushed too hard and is too shrill. If, for the odd tune, I want (I do sometimes!) to use 3rd 8ve E, F#, G on a high whistle I revert to my old Generation which is quite sweet there.
Anyway, at the moment my Swayne low D isn’t as suitable as I’d like for slow airs, for example, where I would ideally like it to be sweeter and easier up to the 2nd 8ve B, and I’d also like it to do slurred octaves through the scale more readily than it does. But, as I keep saying, it is new and changing and I am also adjusting to playing it optimally - various tiny refinements of blowing technique need to become automatic/unthought, and as they do it will sound more as I want it. It also demands very clean fingering transitions (a good thing!). For moderate to fast tunes falling within the average tessitura of trad music it works very well indeed and in a large session it holds its own as well as a flute. It’s not easy, but I’m enjoying it!
Re: contact info etc. No. Jon has no website for his instrument making and hasn’t ever done so. He doesn’t need one - I think he is fully occupied without needing the extra work of running one. This YT video interview with him is of interest. His contact details can readily be found online by an appropriate web-search,e.g.. Try searching on “Jon Swayne pipes maker contact” for plenty more info about him.
Edited to add:
Jon concentrates on his various bagpipe models and doesn’t make very many whistles, especially the low ones, which are dependent on availability of suitable timber amongst other things. He seems to make them in small batches and had obviously made a few earlier this year. His current list price for the low D is £650 GBP before carriage (at cost) and of course the chance of having to pay import duties if it’s a foreign purchase outside the EU. I have no idea if he now has any left. He offered me the choice of Box or Mopane, so there was at least one Mopane one in stock when I bought this one! 
I’d waited quite a few years, not exactly on a formal waiting list but intent/interest expressed when I bought my high D (for which I also waited as I enquired at a time when he wasn’t making any at all!), and then saw on Facebook that someone else had just acquired one, so I jumped in quick!
SFAIK they aren’t available retail anywhere unless you are lucky enough to find one second hand - very unlikely. You have to contact the man.
The Von Huenes I played were from back in the day when Frederick (is that how he spells it) was the company. I don’t recall the original models. But I’m sure you know what I meant by super.
