Just curious! What do you call bumpers (fenders) on a tractor if you call "mudguards" fenders?
Some early British 135"s did have round mudguards :-)but I think they were an option.
Personally having had tractors with both types I prefer square mudguards. I find they give more protection to the operator and they make the mounting of certain things easier. e.g. lights, a chainsaw carrier etc.