I would take a well trained mule over a horse any day. However, I would never get involved with a half trained or badly trained mule. They are either the best partner you could ask for or hell to deal with.
Whatever you do with a mule, the mule really has to love it. They won't run a pattern because the rider says they should. They will only run if they like
to run. Endurance mules are the same way. Either they love jogging the trails or they won't do it. One of the greatest CTR horses I've ever met was a mule. He adored his job.
A well trained mule takes a wonderful trail partner. They will take care of their rider, pace themselves on long rides, don't tend to be afraid, and are generally just sensible animals.
If you want to buy one, try it out. Evaluate mules on an individual basis and don't think you can fix one with issues. You CAN fix them, but it is so much harder than a horse and takes so much more time. Horse people have a hard time training mules because mules aren't horses.