I've never seen any photographic evidence of WW1 carbine use.
I imagine that even pre-war, any cavalry or yeomanry unit in an active operational environment with a risk of actual combat (i.e. North-West Frontier, Middle East, etc) would have switched to a more effective MLE.
The school CCF I was in still had half-a-dozen or so of these - or something very like them - in the mid-1960s. They were issued to boys small for their age who would find the No.4 difficult. As far as I remember, they could chamber drill cartridges in Weapon Training, and fire blanks on Field Days like the No.4s, but (like all except about 10 of the No.4s) were never fired live. I may stand corrected on that, though.