I imagine you chose the Marathon Plus for its ability to absorb endless abuse rather than its comfort.
I don't want visitors messing about trying to repair a rear wheel puncture on a wheel with hub gear and Chainglider. I left the lightweight Marathon Supreme tyre on the front as I reckon the only thing they can mess up is the Shimano dynamo connector, which is cheap to replace.
In the 40 mm nominal width I use on this bike, Marathon Plus is less horrible to ride than in the 28x700 size on the old visitor bike, quite accceptable for the short distances on the island.
I also changed the rear tyre on the other visitor bike, 50 x 559 Dureme to 50 x 559 Marathon Plus. This bike has a roller brake and tensioner (not possible to fit a Chainglider), so the same logic of trying to make it idiot-proof applies. Last year the Dureme rear tyre suffered a puncture, I was lucky, because the visitor knew how to repair it without removing the wheel.