They'be taken a hit in the overall transition to MKII. However I think that, compared to other mercs, they're still competitive - just don't forget to bring Shae along with the Cannon.
They do have some really bad matchups. I know they struggle with a lack of magic attacks. And if your opponent can remove your character models most of your synergy goes with them.
Check with Lou about what to be careful of, he's played them in the past.