I'm not sure they would hold up on a muzzle loader. The recoil process of a muzzleloader can be very hard on scopes.
I have a disc elite and have it topped with a 3x9 Bushnell elite. A lower power such as a four power fixed would work well too. But if you are serious about your hunting and don't want to blow that shot of a lifetime go with a quality scope.
The general rule of comparison is that the scope equal about as much $$ as your gun. I know that sounds high, but what you see is what you get and the scope does that important function for you.
If you are young and have good eyes before buying a cheapie go with quality open sights before getting a scope that is going to let you down.
Just my two cents/ and experience