I consider Maille mustards as mass market, and I like them fine. More bite to their Dijon than Grey Poupon. And I could eat the grainy stuff with a spoon. Tin mustard (the brand, not the metal) is very good, but Maille is okay enough that I don't need to seek it out. (Mustard we do use.)
I'll admit that I'm a Colman's man. I always have a tin of Colman's English mustard in my pantry and I use it like some would use French's.