I have a pair of Geox mules (you can see them in this picture
here). I wanted something neutral, comfortable, and easy to slip in and out of. I found that I cannot wear them without socks. They end up rubbing against my pinky toe--quite uncomfortable. Also, not a ton of arch support, which ordinarily wouldn't be a problem--I'd just slip in my orthotics, but with them being mules and all, I can't do that. However other closed slip-ons look pretty comfy.
I've had better luck with Gabor, Pliner, and Cole Haan in terms of driving mocs. But you never know!