This. There are a lot of important point in there. I'd also add that people who stutter aren't a homogenous group. Everyone's stutter and their experiences with it are going to vary from each other. Things that might work for me, won't work for another person with a stutter. Because of this, I'd say, if it's not just a quick one-time encounter, I'd always vouch for asking the person who stutters directly for their opinion.