The "reenactor powder" is simply not as uniform as the better grades of GOEX, so you could have some variations in muzzle velocity, which won't mess with recreational shooting of round ball, and at smooth bore ranges, will do fine on deer. It's not a cheaper formula or floor sweepings or anything bad. It is not strictly for blanks either. It is made to reduce the overall cost as many reenactors shoot about a pound of powder per weekend reenactment, and the costs add up at that rate. Standard GOEX if I attend one event a month will run me $277.00 a year, while reenactor powder will run me $144.00.
Now if you are shooting in a competition, and you are going out to 100 yards, AND the difference between shooting an X vs. hitting the 9 or 8 ring will mean the difference between taking home a prize or not..., you then need much more uniform powder.
You don't need 4Fg for a musket..., in fact unless it's a small lock, you don't need it for rifles from .50 caliber and up. Muskets were built with the idea of using a uniform granulation of powder for both main charge and prime. You could shoot 70 grains of reenactor powder (2.5 drams) or go up to 80 grains (3 drams) and it will be fine. You can use the same powder for the prime.
LD