From what I recall (and I may be wrong) the McDs versions are "idiot proofed" in ways that the other restaurant machines aren't.

The complaint is you can't de-idiot proof it, even if you know what you're doing (and some McDs franchises are owned by people who run other restaurants with the other machines).

It's quite possible that McDs requires these idiot-proof ones because the risk of "someone got sick from the ice cream gonorreah machine" is too high.