I don't know if they're harder, but it's all I've ever hatched besides quail and one tiny batch of banty chickens. I've had real good success. The main thing to know is they take a week longer, and the shells are harder so it takes them longer to actually hatch. From pip to hatch, it's about two full days.
Other than that, some folks say to incubate them at a higher humidity, but I personally think that's bad advice. I incubate mine at a VERY low humidity (mind you, I live in the humid southeastern U.S.--different environmental conditions call for different incubation practices--this is just what works for me) and get nice air cell development and much higher hatch rates than when I used to follow standard humidity advice.
They do want high humidity during the hatch portion of incubation. I raise it until it condensates slightly on the inside of the windows.
Some folks say to hand-turn them, and apparently some folks have bad luck with auto turners, but I've always used auto turners and always had good rates. My rates tend to be between 80-95% except when there's a specific problem that arises to lower it (like old eggs or high humidity due to external circumstances). I think the hand-turning advice may be useful for hard-to-hatch breeds like call ducks, but maybe not so important for other breeds, but I really couldn't say. Just that auto turners work just fine for me.
Also, some advise to spritz them with lukewarm water daily, and I think this is probably good practice, but I haven't tried it yet. I have such great hatches I haven't felt motivated to go to the extra trouble. Maybe next time. lol
Good luck! Ducks are cute.