I have been using still air incubators to hatch ducks because they need more humidity and the forced air dries out eggs more and because the fan costs as much as the incubator (incubator was $40, egg turner was $40, then another $40 for the fan made it too expensive). I just picked up a used (for two weeks with infertile eggs) Little Giant with forced air incubator with turner for $50 so I am going to compare it with the still air.
I use a separate incubator for hatching so only one gets dirty and I can keep it set up for hatching temperatures and humidity while also staggering my hatches in my incubators. I have pretty good hatch rates and I have come to realize that eggs that don't hatch usually have defects that may have nothing to do with the inncubator. I did a few assisted hatches and ended up with leg problems and even mortality in the ducklings so now I leave them alone and take the loss as an egg rather than investing in a duckling that will most likely die after hatching or have other problems that require too much of my attention. I want strong ducklings and the incubator gives me that, whether or not all the eggs hatch.