Best level 6 unit.

Useful, but it doesn't drop often, and there's also a chance that it won't drop at all...

If the army consists only of Nags or only units from the Tower, there is no chance at all – all troops of the same alignment get +1 to morale. I don't see the point in mixing troops from different castles – morale drops, and besides, the second castle doesn't appear right away, and there will be fewer units from it.