I have used both the Radio Shack model and a more expensive Klein tool model. Both are a royal pain in the a$$ to use! I used the Radio Shack to do my wife's case window and 3/4 of the way through it, the stupid tool broke where the handles are put together. Of course that caused a major pinched finger, a lot of swearing, and me taking it back to Radio Shack for my money back. I finished her window with the jigsaw. My hands were blood red for several hours afterwards (and no, my hands are tough skinned from being an electrician for 15 years)... Her case is made by Casedge (metal)...
I used the Klein model to do my Directron SF-201B case (aluminum). It cuts the same as the Radio Shack model, but with beefier grips than the Radio Shack model. The tool felt much more confortable in my hands, however, it still blistered them... I originally put a PC Mods 11.5x11.5" window in my case. I cracked the window though drilling the blow hole in the side so I had to order another kit (yeah I know its cheaper to just buy the plexi somewhere and make your own, but I would rather just order the kit and be done with it!). The new kit I ordered came from FrozenCPU and this kit was a little bigger (12x12). I did not order the same kit from PC Mods cause I did not like the way the molding fit on both my wife's case and mine (didn't feel snug and the molding kept wanting to turn out)... This time however, I used the Rotozip to enlarge the window. Thats what I should have used the 1st time as that cut through the aluminum like butter! BTW, the FrozenCPU molding was much beefier and holds the window in like a champ. I also used the Rotozip to cut the window in the plexi (used a holesaw last time) and that was a breeze as well...
So to get to the bottom of the story here, just use a dremel, rotozip, or jigsaw with fine tooth metal blade and save yourself the trouble, aggrevation, and very, very, very sore hands....