Pros:
Muscovies are _much_ quieter than my other ducks, which are runners, Hookbills, and calls. Males whisper, females trill.
Cons:
Claws are very sharp so if you are holding a Muscovy and she panics, you will get scratched/stabbed. Those claws are fully functional for climbing and landing and roosting in trees.
Muscovies fly, especially the females. The males are too heavy to fly as well as the females, but they can surprise you! If their pen is not covered they will sleep on your roof, or on your neighbor's roof, or on the roof of the filling station six doors away, which is how I got my first Muscovy "rescue"--her owners got tired of tracking her down every day.
Pro or con, depending on how you look at it:
Muscovies have a much longer hatch cycle (35 days compared to a duck at 28), but they will hatch out and care for ducklings, and in my experience they are good moms.
Muscovies are not mallard-type ducks, so any offspring from matings with mallard-type ducks will be sterile.
The Muscovy males are as big as a goose and more intimidating. Visitors may panic. Males hiss even with friendly speech, so it can be difficult to know if they like you. Females are more shy. However, once they know you they can be quite friendly. My son and his friends spent many happy hours, beginning as a toddler, playing in a backyard shared with a flock of Muscovies. When the children got loud the Muscovies just moved away.
Hope this helps!