That tightness is normal for the Spitfires. If you look at the blades, there is a small hole in them. If you look into the slot where the blades fold into the body of the broadhead, you will see a small metal plate. That plate has a small dimple in it which locks into the hole in the blade and holds it locked closed. The tightness of the blade is performed by the dimple. If you tighten the screw, it torques that plate and moves the dimple away from the blade. As Bowfanatic stated, you can open and close them several times to make them open easier. All this does and wear down the surface of the dimple so it doesn't hold as well. The blades may open in flight but I don't know at what point that will happen. When you buy the replacement blade pack, it comes with the blades, the plates and screws. Take a look at one and you will see what I am talking about.
Having said all of that. I have used them in the past and they worked fine. I'm currently using the Scorpions and they are working well also but they use a rubber band. NAP just makes quality products.

Steve