That microscope works fine, you might need to move it a little to get a clearer idea of a larger area, but FOV isn't that important for this application - the surface area you are checking is not that large anyways. 100X you'd hardly use though. I mean if they have a 30-60 that is the same price go for it, but don't stress over it. Just sample from a couple of different locations. I have used/am still using that exact microscope for going on~ 6 years or so - Don't fix what ain't broke!