Zulu Problem (Not quite what you think)

[beetle]

Or are the buffalo promos so good that I won't miss March?

The first one, the extra move, is quite OP. But I get them all because the window is short and it is fun to do things a little differently.

...especially since they can promote to Muskets whilst the Impi have to wait for Rifling.

That is a very good point. If you have only Impi, there are many turns between Civil Service and Rifling. So some Ikanda-buffed Muskets to hold the line while waiting those last dozen turns before the Impi upgrade can help keep all the Impi alive to the end of the game.