Are Niefel Jarls too strong?

[Endoperez]

But they are mages, and could do something at your lab. They are useful, but they cost a lot. How much upkeep do they cost?
And, how useful they are as (combat) mages? They can cast quickness to themselves, and to others in late game, but what else?

I think they are good, but it might be better to use most of your income to buy normal Jotun commanders instead. They are sacred, lot cheaper, and can equip those items as well as your Niefel Jarl. But NF does have a better magic resistance. Complicated. And very, very interesting.