Mine spins freely, in fact I need to oil it a bit as it's dry. I suggest you place a few drops of a light oil where the ring meets the body of the compass, let it sit overnight and then try to rotate it. I note that there are screws on the bottom holding the unit together, and you might need to open it up to access the guts. In any event, you need to lube the ring since both the ring and the body are aluminum and I can feel the galling one gets when you have to bits of Al moving against one another.
It is not actually a prism, it is a straight-through optical diopter sight. Kind of like a microscope. The original K&R/Eschenbach/Wilkie brand German march compasses on which these compasses are based utilized machined threads in the diopter housing and you could adjust the focus by rotating the black eyepiece. This compass may have either a nonadjustable eyepiece or one that is improperly constructed, thus may not be adaptable to your eyesight.
I have looked this thing over and cannot tell you. I threw away the packing material so there went any clues as to country of origin. I searched the internet for half an hour and still can't tell you. Huntington seems to make their own stuff, I think in the USA.....couldn't swear to it though. It is a very nice compass though, well worth the money.
These dimensions are for MG1 are approximate and taken with the unit closed: Back to front it is 3 1/2 in or 9CM. Side to side it is 2 1/2 in or 6.5cm. The unit is 1 1/4 in or 3cm high.
Hope that helps