There are defo 2 types, they've got different seals for the different fluid used and different sized pistons to match Shimano or SRAM levers, from those differences you've also got post mount, which is the same for front or rear, or flat mount, which is different for front or rear.
The shop seems to think the hope rx callipers are universal front and rear but I was under the impression their are two types ? Anyway ordered