The difference between a UWAN and your average non wide field eyepiece (other than the UWANs bizarre shape) is that a standard eyepiece will yield around 50-55 degrees of apparent field of view, the UWAN easily trumps this by offering the observer a whopping 82 degrees to gaze through.
This makes the 16mm UWAN one of the most versatile eyepieces I've used. I can use it on the moon and planets, the wide field means I don't have to realign my telescope as often to keep the object in within my field of view. Not only does this limit potential frustration but when your brain has been freed from the repetitive manual process of shifting your telescope along every few seconds you can actually pull out finer details especially in the planets.
I can also use it on deep sky targets, in fact the UWAN is perfect for open clusters (interestingly grouped stars that are bound by each others gravity). As open clusters are usually quite large in the sky (relatively speaking) the extra field of view comes in handy to frame the clusters making them look like islands of stars.
As well as OCs the 16mm performs incredibly on other deep sky objects, my particular favourite use so far has been to point my telescope at the Virgo supercluster and pop in the U-ltra W-ide AN-gle piece. The Virgo supercluster contains as many as 2000 galaxies packed into 30 degrees of sky, for reference if you hold a clenched fist at arms length this is roughly 10 degrees.
With the 82 degree apparent field afforded by this eyepiece you can pretty much point to a random position within the supercluster and see as many as 20 galaxies in a single view!
I was a little sceptical before using the Uwan series, to obtain that extra field of view Williams have had to use 7 lense elements, that's three more than a similarly focal lengthed but non wide field eyepiece. Usually in Astronomy the less glass you put between you and your target the better. Thankfully my fears were misplaced, Williams have used quality glass in their optics. The views I have had are tack sharp and crisp as any plossl, and the sharpness continues right to the edge of the field.
The whole series of UWANs are parfocal, this means that once you've achieved perfect focus with one UWAN then all other UWANs will be almost perfectly focused to. This may not sound like that big a deal but certain focusers can produce alot of shaking when they are adjusted which is a pain especially at high magnification. This ensures a minimal amount of fussing when changing eyepieces and is a great feature within the series.
It's amazing what Williams have done with the UWAN, the end result is a wide field budget eyepiece (being careful not to call it cheap as it's anything but) that can keep up with the giants of the wide field fraternity. Gone are the days when wide field "spacewalk" eyepieces belonged to the rich, for around £150 ($300) the UWAN is an absolute bargain.