I have both a UKPN and an Orange Urban.
I love the blade shape of the Urban. However, when in hand it feels like a "gentleman's knife". Do not get me wrong I am sure it is functional for daily use (it is a Spyderco after all). It is just not the size I choose for an EDC. In fact if it was not Orange I might use it as a "dress knife". Black G-10 with the low riding clip would really disappear when clipped to the pocket of black slacks.
I love the size of the UKPN. It is perfect for my daily office life. Which means the following:
Large enough to be useful in most situations.
Small enough to not cause "people" (I use that term loosely) to run screaming to HR when I use it in my cubical.
It does not have a lock so again "people" do not think "OMG HE HAS A KNIFE!!!!"
I have never held a UKPK, what is so much more desirable about them over the caly 3 other than being made in the US and having S30V sttel? It seems people like them more than their caly, but why?
Personally I rather no lock to most back locks. I would say the order of my lock preference: Compression, Frame, Liner, None, Back. (I have never owned a Axis Lock BM or a Ball Bearing Lock Spyderco which seem to be the next most popular.) The UK outlawing locks has (in a very perverse way) made me happy because we are seeing Slip Joints from Spyderco which is just fine by me. The Spyderco designers did a fantastic job with the slip joints.
All in all both are good knives. I like them both but for different reasons. I would recommend either to a friend wanting a good EDC. I EDC the UKPN for the reasons stated above.
Hope it helps,
STICF