I use them for everything I use chicken eggs for.
Stubbornly. Because they are harder to peel. So boiled eggs can sometimes be a bit of a challenge.
I do not notice a fishy taste. I would describe them as more rubbery. The eggwhite is thicker and less salty and more tasteless then chicken. It has way more eggyellow though. And eggyellow is awesome. But it runs less then chicken egg-yellow. So no awesome fried eggs with runny egg-yellow :'(
I prefer chicken eggs. They are more moist and less rubbery and have more taste. Some people I know prefer duck-eggs. I asked them why but they could only answer 'they taste better'.
So I guess you just have to find out on what side you are
Due to having too many duck eggs we force-shower everyone we know with duck-eggs. 90 procent reacts with 'they are not much different then chicken eggs!' and 10 procent with 'they are way better then chicken eggs!'. But 0 reactions how they hated them.
The only advantage I noticed where they overrule chicken-eggs; meatballs, dough, and other stuff where you have to mix in a raw egg to make structure. After I found that out I also met a baker. Well, I had met the baker before; but he learned that I have duck eggs. And went crazy. Apparently bakers use for years duck eggs instead of chicken eggs because of better baking results =/