Here are some pictures ...
The first two smaller images are where I compare normal on left with mule on right. The larger image is yours rotated and cropped (using PhotoScape), and looks like a normal coin to me.
The three quickest ways I use to tell is the COROIN word - depends if the C is further forward i.e. closer to the left (above the shoulder of horse) on normal coin. Then if the OI are further apart that also is normal. So the 'mule' is further back and has OI closer to each other. Thirdly the mule has thinner lettering.
P.S. Now I look at those two smaller images I also see the LEAT word helps. On a normal coin the top of the L points slightly downwards, and on the mule it points slightly upwards. Hope all helps - and I have no idea on value of a set - I go to NGC for individual coin values.
http://www.ngccoin.com/poplookup/World-Coin-Price-Guide.aspx