They have been selling out like crazy in my area, and my dealer has a hard time keeping them in stock. Here is my dilemma: I have two M&P 45's, and my buddy has a 21sf that he has never fired. He offered to trade me straight up for one of my M&Ps. I am wondering if I should trade for the SF (I hate trading guns usually) or wait for my dealer to get more Gen 4s in. I have Gens 2,3,and 4, so I know the difference. I am debating on holding out for a gen 4 21 or making this trade for the Gen 3 SF. I would appreciate input from those who own, or have owned both. Thanks for your time. Frank.