Those aren't mules, at least not the one that held the name brand.
Mules had iron wheels and were built in Alabama (selma or troy I think). My father had a dealership on them in the late 70's. They eventually went out of business. He still had one I gave him a few years back, that a friend gave me. I don't know if he still has it. They do not have the front wheel and balance wonderfully. They were equipped with a gear reduction drive and 3 1/2 horse power B/S. You had everything from cultivators to a turning plow you could get for one....And yes, they would bite in and dig. Rubber tired knock offs and front wheel supported ones were not "mules". The true mule was patented and trademarked. I will see if I can find a picture.