In Civ5, when you have access to iron, does it make sense to build musketmen?

Technology upgrade tree looks like this:

|Steel          |    |Gunpowder   |
|- Longswordman |    |- Musketman |
|  cost 150     |    |  cost 120  |
|  str: 18      | => |  str: 16   |
|  mov: 2       |    |  mov: 2    |
|  req: steel   |    |  req: -    |

Therefore, at first glance I thought that since the Musketman is a unit for a later technology it would be "better". But it appears that as long as I can build longswordmen and have the time to build them, I should not spend maintenance on musketmen.

Am I correct? What about upgrade paths?

Solution 1:

You get a -50% penalty if you are using a unit that requires a strategic resource, and then go negative in that resource.

That is, you lose a source of Iron that puts you below 0 Iron, all units that use Iron will have a -50% penalty until you get more iron or lose some units.

This is especially annoying with Aluminum and Uranium if you have puppet cities that use those for buildings. If you get in a war and temporarily go negative, all of your nice units become expensive rubble.

As per your original question:

I ignore musketmen in general. It's not worth the switch if I can have a unit with more base defense. that, and it's a pretty easy jump into rifling at that point.

The point of the musketmen is in situations where you've got no iron available but need units. They'll do in a pinch, since horse-based units are easily countered with cheap pikes or spearmen.

The french and the americans have unique units instead of musketmen, so they are more likely worth it.

Solution 2:

As shown in this question the upgrade paths are the same. So I guess it comes down to whether you are willing to wait the extra production time, and whether you have a better use for that iron. Besides building other units with it, keep in mind that you can also trade it to a friend temporarily for an economic boost.

The other factor is that if you are under attack and you lose some sources of iron, you could start suffering a penalty to combat power if you go negative, which is less likely if you stick with the musketmen.