They are disease resistant and are more tolerant of heat and cold. Founder and colic are rare in mules, thanks to built-in mechanisms inherited from the ass. All in all, it costs less money to keep a mule. Mules tend to develop trusting relationships with the rider or trainer. Many a good mule has been ruined by one single fit of temper.
Mules are generally more intelligent than horses.
Mules and asses both share a very well developed sense of self preservation. Seldom will a mule allow you to put him in a dangerous situation, nor will he allow himself to be overworked. If the mule trusts you he may accept new and strange situations with little question, but when he balks the wise muleskinner investigates before pressing the issue. A recalcitrant mule could be warning you of danger. Caution in a mule is often mistaken for stubbornness and the uninitiated usually wind up regretting any attempt at forcing the animal to submit.