I don't hunt turkeys, but I carry an Olt's CT-220 cranker in my console to annoy turkeys and groundhogs as I see them on the side of the road. I usually prefer an unaided mouth call for turkey, but the Olt's cranker is a favorite of the groundhogs.

The problem I have with box calls is getting them to be quiet when they are in my vest. They tend to rub around and make odd sounds. With slate calls, you put the striker in one pocket and the slate in another pocket and that problem is solved. Dean is right, though, that a false strike with the slate call is more obvious to the turkeys. I have not used a diaphragm call, because a friend of ours almost choked to death on one. My Dad and brother swear by them though. I have a wingbone call from my first turkey, but it is too much a work of art to use heavily. You just have to find one that works for you, though.

I am seeing the turkey calling thing is like SXS shotguns you really need at least a dozen. I always laugh when I hear Jeff Foxworthy response to his wife asking him why he needs another gun.
" Didn't you just buy a gun last week?"
His response, Yes Honey but that was a short range weasel gun, I need a long range weasel gun. LOL