I feel the same way. I'm not comfortable with mini equine service animals. They are kept isolated from other horses. Despite 'special shoes' I'm not comfortable with a hoofed animal being on a lot of the surfaces they have to work on. The feeding routine also, I have problems with. The use of dwarf animals too, to get the size down to the minimum, I feel has its risks. Dwarf mini/horses have some serious health issues and issues with their joints. The most critical thing is they can't go for long periods of time without eating or they may get fat embolisms.
When I see most of them working, to me they look rather disspirited and not in good condition.
There are some interesting books and articles surfacing about the ethics of service animals, but a good many of these materials aren't that new and some people who care about animals have urged caution for a long time. I don't hold, though, with the extremes if this point of view, that we should not have any companion or working animals.
I don't expect everyone to agree with me, but I have an increasingly uncomfortable feeling about service animals. I feel enough of the people involved don't have a realistic understanding of the animal's needs or the effect on the animal of doing service for disabled people. I was extremely surprised to see this problem in higher-ups and certified people from a national organization.
I was very impressed with one riding for the disabled stable I volunteered at, they felt doing service work was very stressful for the horses, so they had six week long lesson sessions, and between those times, the horses are turned out in a herd.
So I feel caution and concern for service animals is very important. I think with the right approach it can be done respectfully and with the animal's needs in mind.
But using minis as service animals in buildings in the city, that, I can't endorse under any circumstances.