Crow flappers (aka Buster): Ive used them plenty and they work ok. They do not deter crows from coming to your spread like a mojo will but I am not sure if they will INCREASE your crow take. They are a good tool, but also note that I have not used mine in two years.
About your decoys: Hot water and a scrub brush is good if they are just dirty/dusty. Flocking is nice and will really make them look good. The old standby, however, is to just clean/scrub them and paint them with flat black spray paint. Works fine.
Ureaduck Flapper decoys, bigger than the Buster but works great, has more detail. Just don't hit it with shot it just don't hold up. Knocked a wing off of mine Saturday. Luckily its a glue-able fix, I hope. It looks like Ureaduck no longer makes the 3D Flapper Crow.
With very little effort; electric tape the head, hot glue spring on battery cover, these can be modified and set up exactly the same as a Buster II at a fraction of the cost.
The problem I have ran into with the flapping deeks is the fact that they just don't last. The motors just qiut on them and you are done. I bought 2 of the assault crow systems from ureaduck. You can make them move with a pull cord and don't have to worry about motor break down. I am anxious to try whitenuckles boondocker, in October. Elk if your deeks are not flocked. Buy a flocking kit and coat them with some flocking. I think it makes all the difference in the world on a feeding set