I think they are very versatile in how they can be used, fitting with the theme of the faction. So it’s going to depend on the scenario, and the builds of both armies.
They obviously make great filler units.
In objective based scenarios, I like Valorel’s thoughts on how to use them.
In more combat based scenarios, I’m torn a bit between putting them on a flank, or more towards the center. Flanking would help give their stats a boost, while the center gives them some protection and options on movement.
I think opponents are going to put them into one of two categories. A weak unit that can be ignored, or an easy target to take out quickly. Knowing your opponent, you build, and the scenario will help guide you on how best to either exploit or mitigate those viewpoints.
Pairing them with siege weaponry, as you mentioned, does make a good combo to offset each other’s weaknesses. I think having Aemon as an NCU would be a good pair as well, to make them even harder to finish off.