This is my first design that started it all, the first model was quite small and with a more rounded handel.
But over time it has changed more and more. Two of the key features with the design is a finger choil inline with the pivot, and the jimping on the blade that protrudes over the handle when the blade is open.
The original blade shape is a modified wharncliffe. 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 has the Spydiehole for ease of use.