Typically they are only used for Trap and Skeet Shooters and the full barrel length cylinder are the best and come in sets. (.410, 28ga, 20ga, ect) Over/Under guns probably the only worth while to use them on. From what I've seen anyone with these isn't as good of shot as they think and don't really need the challenge of smaller guages.

They probably make them for 870 if you wanted, but they would cost much more than the gun.