Nice dagger, indeed, though a bit more V-42/First Special Service Force, than Fairbairn-Sykes. The First Special Service Force soldier held his V-42, with his thumb on the flat of the choil area, for at least some uses, therefore the notched area in the V-14’s guard. The V-42 did not have a notched guard, but does have a thumb rest on the flat of the choil area.
I found this link, that shows how a British Commando held his F-S:
https://www.youtube.com/watch?v=uDGHKyB3T_U
An F-S can be held like a V-42, but the V-42 and V-14 are built to facilitate this particular hold.
Notably, there is a newer dagger being sold by Spartan Blades, a collaboration with William W. Harsey, which also looks very nice.
https://spartanbladesusa.com/shop-al...harsey-dagger/