I've been around mules my entire life, mostly driving teams but there have been a couple of riding mules in there as well. Personally, I prefer a good horse because I don't understand the way mules think. They are incredibly smart and they really think about things. I second everything Brighteyes said, if you are going to get one, get a good one with no issues. When a mule is good, they are **** good and when they're bad, they are hell on wheels to try to deal with.
The ones that we rode, we just used regular tack on them and had no problems. One thing about mules, their gaits feel different than a horse's. They aren't better or worse, just different and can take a bit of getting used to.