I have adjustable peeps on 3 of my muzzleloaders. I am able to shoot up to 200 plus yards with them. Some guys I know can shoot 300 plus with theirs.
I have red dots and reflex sights on some of my 100 yd and closer guns.
I’m a traditionalist with my muzzleloaders, but if you’re asking what will be most effective, the red dot is leaps and bounds more effective, in all conditions. It’s far faster, and will allow precise shooting in any lighting or background.
I’d put a caveat on this, that someone really has to put in the work to build up a load with most muzzleloaders for them to be accurate enough to get out past “holding hair” distances with a red dot. Most guns and guys in the field just won’t be getting beyond 200yd accuracy, to where dialable peeps would really become an advantage. Broad generalization for sure. But for most guys, I’d want to see them keep a patten inside a plate beyond 150 before an RDS would be the lesser choice.