In my personal experience I'd say if a person only has one snake it most likely would not be in a tub. It would be in an aquarium or some type of enclosure.

I don't think they take to one person, they act the same to everybody.

I can't answer about letting them roam, I've never tried that before.

I would say that they should not be kept in water unattended. When people soak them they only put enough water to cover about 1/4 of the body. So they technically aren't even swimming.

Thats my personal opinion, I hope it helps.