The problem with just shooting at a turkey head target or any other small target is that you can't see what your whole pattern is doing or where your shotgun is throwing the center of your pattern. Trust me not all shotguns (even really expensive ones) throw their patterns perfect to the point of aim of the bead sight. Also different chokes and shells can shift your point of impact too.
Do what you like but you can shoot the same shell through the same gun and choke at a small turkey target and get 6 radically different results never knowing what the heck is going on. Did you pull the shot? Was the center of the pattern high, low, left, right? Who knows unless you shoot at a large sheet of paper. Only then can you truly tell which shell/choke combo is throwing the best pattern and whether you need an adjustable sight to get it centered to point of aim.
And it's not like it's a major expense to shoot a sheet of poster paper or a section of craft paper. If you like you can still tape a turkey head target in the center of it. But one shot at a large sheet of paper will tell you more about what you, your gun, shell and choke are doing than ten shots at a can or small target.