Two hens each with their own chicks are in the field are looking for insects.
The one hen find one and calls to her chicks. Do you think the chicks of the other hen would come to that call?
After a month or so of that they will recognize the call of the mother hen for sure.
The Tom also recognizes the call of a particular hen so if your call happen to mimic closely the pitch of that call, he has no reason not to come, whether it's a cheap call or an expensive one, as long as you are using it right. Of course some are just gullible and want to come anyway.
You can also teach a Tom by association using the same call over and over again and a bang to go with each time. Soon the same Tom will shy away from the same call or decoy for the same reason.
This is just personal field observation nothing more.