I've had toms come in to hen decoys as well as hen/jake decoy sets. When I use the set, the tom always goes for the jake first. Last year, I had put out a set, and the tom came out of the woods behind me into the field and went straight for the hen. When he got about halfway to the hen, he then noticed the jake I had placed inconspicuously in some grass in a laying down position. He changed directions and went toward the jake, which brought him 20 yards right across the front of my prepositioned gun barrel.
I think sometimes the jake decoy will keep them from coming in from a distance, but in my setup, he didn't know he was there until he was already committed and had to defend what he had already staked as his own. Unfortunately, I didn't set it up with that intention, but that is how it ended up working out. Whether you use a jake or not is a personal preference, but they can give you the results you want if used in the right time and place.