The type II allows for the EVS coupling to be locked out or in as desired. If you look at the middle of the aperture dial, the first type will have a silver circle. Pushing this in disengages the EV lock, allowing you to adjust the shutter and aperture separately. When you release the center circle, the EV system locks back in. On later models, there is a silver oval, not a circle. You can push the center in and rotate it to disengage the EV system, and it will stay disengaged.
I would not let this define which camera I buy. I would let overall condition be the determining factor. If I had two cameras, one type I and one type II, in equally good condition, I would take the type II because I personally do not use an EV system. But the reality is that you will quickly learn to push the center button without much thought.
I think Rollei found out the answer- people like to be able to choose whether to have the system engaged or not. So they modified it to allow this option. I have a 2.8C where you need to push a side tab to change either shutter or aperture settings; some people do not like this at all, but I got used to it quickly. Many Hasselblad lenses have the EV system and people still use them. Sure, it'd be nice if it can be locked out, but you'll adjust. Get an MX-EVS in good condition and the EV system will fade quickly as you enjoy a great camera.