The paper vs plastic issue is unimportant, in my opinion. In fact, the latest designs I've seen are made of polypropylene sheets instead of paper sheets.
I think the critical element is that it's cheap to build and ship.
Again, what microscopes do you know of that are cheaper?
I do like one thing, this has the potential to inspire kids about optics. I sure would have loved to have one growing up!
These point of care services aren't limit by the cost of the microscope, they are limited by staff and the cost of histology. Most of the scopes I see at the clinic are cheap brightfield ones used to look at stained specimens, and are kept as backups when the Beckman-Colter machine fails. Can your microscope distinguish white blood cell morphology? Working with live cell imaging you learn that red-blood cells are evil because they carry no detail and little information, they are trivial to see and deconvolve. You can see relevant features even if you are beyond the diffraction limit, but then again you need those fancy slides that spread the cells out so that you can inspect them one-by-one.
I think the critical element is that it's cheap to build and ship.
Again, what microscopes do you know of that are cheaper?