This is my first design that started it all, the first model was quite small and with a more rounded handel.

But over time has changed more and more. Two of the key features with the design is a finger choil inline with the pivot. And the gimping on the blade that protrudes over the handle when the blade is open.

 

The original blade shape is a modified wharncliff. But there is also room to fit a drop point shaped blade in there. 

I have made Enigmas with both thumb stud, spydiehole and thumb disc. My personal EDC is the Spydiehole for ease of use.