Calls are wonderful, I kept them for many years, they don't make as much mess as the bigger ducks, friendly if handled well, small, nice round duck shape, have a wonderful 'quack' (before I knew what they were I could hear one over the valley and called it a laughing duck) err - just one point, female call ducks can be a bit noisy, but mine tended to be ok unless wanting food, fresh water or I was late letting them out! Go to some agricultural shows over the summer, there are normally ducks about and the breeders would be happy to advise and hope to sell you a pair :-)
They must of course be in a fox/stoat/mink proof house at night, preferably a safe run during the day, esp if dogs and cats could think they are fair game.
Call ducks only lay in spring, quite small eggs, not normally eaten.