The tekans I have are the most reusable mechanical I have ever shot. I bet the three heads I have are going on several dozen shots and have yet to break a blade. The way you reset them is first you have to make sure the blade track is clean. Its the little grove the thin blades slide in. Just take the b-head off and take a toothpick and make sure itis good, foam targets leave alot of stuff in there, not sure how much bag targets leave behind. Now, slide the blades back in and make sure you have a o-ring already slid on the shaft of your arrow. Then screw the blade back on to the arrow and slide the blades until they look about half way deployed. Then take the o-ring and slide it up on the head into that little grove on the bottom of the head, make sure the o-ring looks even around the head. Now take your blades and start to push the forward back to the closed position, this works best for me with a pencil eraser, push on the very end of it until you feel it snap in place. Then you should be good to go!

Edit: I said the most reliable I have ever shot, that is false. Its the only one I have shot. My experience comes from my two friends that shot the kind that fold back. They seem like they were always busting blades and then are back there with the little allen wrenches trying to replace them blades.