Bats, just like birds, actually prefer to poop while in flight, so most of the guano droppings will fall as bird droppings do, out of sight and out of mind. That said, their will be some guano coming out of the BatBnB, which is why we recommend mounting the BatBnB above a low-use and non-edible garden bed or lawn. That way the guano will actually act as a fertilizer for the lawn or bushes growing underneath. The only complaint we’ve ever seen about guano is an individual who mounted their BatBnB right above the door to their house, so naturally they got some guano on their shoes… so that was a bad idea. Some guano may appear on the lower landing pads, but should mostly wash away when it rains. The BatBnB also extends an inch off the wall, so most of the guano won't hit the side of the house (if that's where you want it mounted), and even if it does, rain will help, and if it ever gets too bad you can use a pressure washer in the winter months when the bats are hibernating.
The fungus that causes histoplasmosis is found nearly everywhere, including in most city parks, because it is most often associated with bird droppings. For anyone who doesn’t stir up and inhale dust associated with animal droppings, histoplasmosis poses a very remote threat. Most human cases are asymptomatic. Be sure to wear a respirator and goggles if you ever need to get near a BatBnB that has been occupied. Unless you are a trained animal professional, never go near a BatBnB that has active inhabitants - they may get scared and choose to defend their pups.