There are some minor differences beyond the lock.
-UKPK has a slightly deeper carry pocket clip for better carry concealment
-The UKPK has S30V compared to VG10, or ZDP189 in the high end Caly 3
-The UKPK has a deeper index finger choil, which most agree is more comfortable
-The UKPK has no liners, which makes it much lighter
-The pivot screw of the UKPK doesn't stick out quite as much as on the Caly 3
-The UKPK is all screw construction and can be fully disassembled. The Caly 3 has pins, except for the blade, which is held in place by a removable screw.
I prefer the UKPK to the VG10 Caly 3. Mainly due to the lighter weight, S30V and deeper finger choil.
The UKPK does open quick and easily, but it has a half stop so it won't feel as smooth as the Caly 3.