Hey Bri,
Travel for the shoe is more tied to the gradations within the scanner than it is to the shoe itself. The travel of a potentiometer is pretty standard. What the scanner does with the voltage change is another matter.
When we updated our CMK2 firmware recently, one of the things we did was increase the crescendo stages from just over 30 to over 40 possible gradations.
I just got confirmation from a user (after reading this note) that our shoes work fine with the Haverhill set. And, co-incidentally, they are available in England
Cheers,
Darryl