Have you already determined that you prefer a digital 2D microscope to a stereo view optical microscope?
The lenses are a bit confusing. You need to scroll down to "Description" and look at the working distance and magnification power. You probably want something in the 100-130x range max.
Look at this video, you can see them demo the "fixed" 130x lens:
Note how they bring the unit closer to zoom, and adjust the lens to focus.
Here is a demo of a zoom unit:
They rotate the lens to zoom in, then adjust the height to focus.
Looking at the lenses above, you can determine if you want the zoom knob (~$80) or not ($15). Zoom goes better with the focusing rack style stand they show in the second video.
For the specs, higher megapixel isn't necessarily better. Usually what is desired is large sensor size and good frame rate.
One issue with the specs is that Eakins has been known to ship falsely labeled cameras. So they might say it has a particular sensor and it will show up with something else.
You haven't given a budget but I assume it is on the lower end? $200-300? Since you don't want autofocus.