Fun and effective...
They are absolutely great on the low end calling (i.e. quiet contended clucks, purrs, and even quiet yelps).
I have been amazed at birds that I can barely hear gobbling, responding to the most quiet purr I can generate. Great way to let a tom know that the hen is still there, but she is not coming to him.
They are capable of generating some volume, but not that of a good box call....