They do (right hand users), watch on left hand (opposite), use mouse with right hand. This device would be on the right hand for those people - the same that they move the mouse with. My question is, will it interfere with using a mouse?

I'm confused then. Why would one wear this and a watch?

Good question. The initial UI displays time. I picked one up today and have been wearing it on my normal "watch" hand. That being said I have been wearing it so that the UI is on the inside of my wrist. Definitely feels more natural when sing the UI.