Collars: It is a choking hazard. It is not painful. They make sure that it's loose enough to not hurt, but tight enough to not be taken off.

Cuffs: They are unforgiving, sure. But you are correct - this is the point. They are not for show, they are for real. Some people wear them for show, but most people have these not only to show ownership but because they are a style of cuff that makes the relationship sometimes more enhanced and permanent. Such cuffs are expensive, sometimes hundreds of dollars, and buying them for a submissive means more than just buying an accessory. They are shackles, also, and used as REAL cuffs. How are they? Excellent, perfect, wonderful.

The d- and o-ring is something to go on a collar or cuffs. It's nothing special, it's just a ring purchased if someone bought a collar without a ring or made a collar of their own.

Do tell me if you have anymore questions!