It is much easier on a slate. To do it on a diaphram you have to vibrate the tip of your tongue very fast but very soft, which is hard to do. I can do it, but rarely if ever do it with the mouth call when hunting. Always the slate, which, on my call, sounds pretty darn close (OK, identical :-) ) to a live hen.

My Dad and I often hunt together and I've had the good fortune of doing the calling from a position behind him and watching him take several birds. In these situations I'm not worried about getting a gun up so I can keep the slate in my hand the entire time, so purring and soft clucking becomes my call of choice. I've always thought that it is a call that tells the gobbler everything is OK, come on in.