Never used one. Actually, never even knew they existed till this post. So here's a totally uninformed perspective

I don't see how they would differ from duck, deer, or turkey calls with respect to alerting birds to your presence. If you can work them well enough to sound convincing to real birds, they may not help but they also probably can't hurt things at all. If (like most duck, turkey, and deer hunters) you have no real idea how to use the call and make realistic animal sounds, then it's best not to use a call at all
