Box calls can be OK on windy days, but for still days when the sound carries well, I prefer a slate call.
The box call has too much volume to suit me and it puts the turkeys on alert just out of range too often for my tastes.
With a nice soft slate, I can manipulate the volume to seem like the hen is farther away and I can "throw" the sounds to the right or left to guide the bird into position.
When they come into range for me, they think they're still about 50 yards from the hen.
Here's a decent video on box calls.