I actually have the Uncle Mikes for my 642 and I paid the extra ten or so dollars for the upper garder support. The garder makes it so you don't need to really crank tight on the holster itself, and helps to keep it both up and in position (oriented) with a wide strap around just below the knee (the calf muscle helps keep the garder up).
Now that I have tried the UM ankle holster WITH the garder accessory, I would not wear it any other way! You are still probably less than about $50 or so!