Better flight.......really, I dont think so. A proper setup will react the same with either head.
Uh, no. I have used both fixed and mech heads from time to time. Fixed heads can of course be tuned to group with your field tips. But fixed heads are not what I would call field point accurate. Even from a perfectly tuned bow if you torque the bow a bit or shoot with less than perfect form it will affect accuracy much more using a fixed head. At 15 yards it's not going to be a issue. At 35 to 45 yards? Yep, it can be. Shooting with perfect form standing on the ground in your front yard flinging sticks at a target is easy. Shooting with perfect form 30 feet up a tree, wearing thick clothing, in 20 degree weather, as you kneel to shoot under a limb at a big buck that has your adrenaline pumping, is another story.
I will concede that fixed heads penetrate a little better but if my bow is generating enough power that I am getting pass throughs with a large diameter mech head then what advantage do I gain by going back to a smaller diameter fixed head? Is driving my arrow 2 inches deeper in the dirt on the other side of a deer really going to help me in any way you can describe? Cause I'd love to hear the explanation of how.