There are bad mules, just like bad horses. Problem is, if you have never dealt with a good mule, you may think they are not worth the effort. My neighbor is an excellent horse trainer, but said he would have given up on my mule. He thinks she uses too much of her smarts trying to avoid learning, but I know she is totally capable, just getting through can be a challenge.
I posted most of my thoughts in another post "mules love 'em and hate em"
I would certainly get another mule, but am hopefully smarter for future training.