They will be as good at laying as taking a rooster out of that RIR flock and mating him with a hen out of that BR flock. The only difference is whether or not you can sex them at hatch.
There is nothing magic about a sex link and laying ability. They are not great layers because they are sex links. They are great layers because their parents are great layers, or they are lousy layers because their parents are lousy layers.
I don't know what a "normal" black sex link is. Some hatcheries sell commercial egg laying chickens as sex links. Those are great layers. They have been bred for many generations to produce great layers.
Some hatcheries cross birds from their dual purpose flocks to produce sex links. Since hatchery dual purpose flocks are usually good egg layers, these crosses are usually good egg layers. They are bigger in size than the commercial sex links and do not get as good a feed to egg conversion rate, but they normally lay pretty well.
Some of us make out own sex links out of birds we have in our flocks. Some of those make good egg layers. Some may be better for meat than eggs. Some may be good at neither. It depends on what we are breeding for and the traits of their parents.