Netter,
They are both 'recognised' variations of the Mk I Rabbit trap. Fenn was constantly making alterations to them - to make them better, cheaper or simply because that was all he had at hand to make them with.
I know another trapper that swears by them - and he knows a thing or two about trapping rabbits. I couldn't get on with them myself - I much prefer the Imbra as a rabbit trap
OTC