I do a fair amount of Crowhunting and own an "E-caller", however I actually prefer using the mouth caller (Quakerboy) because you can talk/respond to cawing crows with greater effect.. I believe that they become used to hearing recorded sound.
On a side note- while Turkey hunting this year I was using the round aluminum slate call and the crows wouldn't leave me alone- you can imagine how that scenario ended..![]()