Primary chains just keep on stretching until the tensioner either wears out or just cant keep chain tight anymore, so you end up with a distinctive rattle at idle, most bikes do it some are just louder than others,
There are various options available ie cryo treated at double the price, or the cheaper vw/audi/porche camchains that others use.
But actually you have to remember yours are probably years old and done thousands of miles so probably a new stock set will be just fine and these bikes are getting looked after now and you probably wont do the high mileage and mistreat it. So just go with these. they will be fine.