I've had enough problems with spores farting when shot that I don't dare build anything that uses grenades. Even Leyden weapons are dicey...
When I ask them from the ministry, they often get deployed inside buildings. And there they stay, trapped.
That's the thing, it takes an insane amount of resources to build just one (seriously, try it, it's breathtakingly expensive), and yet you can hire them easily on a regular basis from the empire with a mere 20 standing points. I think there may need to be some balance changes here.