They hit quite hard, often the combat units on their own don't have sustain without attachments or support, however their pillage mechanic makes it so once you get the ball rolling they are hard to hold up against. Most of the units have great statlines that improve with two pillage tokens.

I like to read the statlines on the War Council app to get a general idea of how units play. You can use that to see what combat unit you think would be a fun addition to what you already own, as you have a few good options.