Musketmen are kinda weak now that I think about it. I might make a few as defenders, but other than that, gunpowder is really just another step to rifling.
Muskets are at a disadvantage vs Knights, 10 str > 9 str.
You generally use a Drafted Musket Army in combination with your Veteran City Raider Army and they make reasonable defenders so you don't have to wait for reinforcements to defend your recently captured cities.
Thread was a bit dead when it started out 
I will build them if I have a lot of gold, just for quick upgrades to Riflemen.
What's weak about them? They're cheap, need no resources, ignore walls/castles and don't have any real predators (like knights have pikemen).

difference)Why not use macemen for this, they can have CR Promos?
and only under Nationalism
Muskets are good, as:
-They are better city attackers than Maces (0.2difference)
-They are stronger than all units except the Knight (which is a very small 1difference and can be countered with Pikes)
better, not 0.2 (Maces do not inherit 10% against cities).
more than maces. With 2 promotions, maces have .8
more than Muskets.the macemen promotion costs more $.
cheaper than muskets...?True enough, though the extraFirst point, raw macemen and raw muskets, muskets are 1better, not 0.2 (Maces do not inherit 10% against cities).
With one promotion (Combat for musket, CR for Mace), Muskets have .3more than maces. With 2 promotions, maces have .8
more than Muskets.
...
But fewer are needed because they are more effective, see above statement. Also, maces arecheaper than muskets...?
for muskets are free if you're getting them through drafting.