Mr Director

I am shooting a film with the Canon EOS 60D DSLR in HD and I would like to purchase a director's viewfinder in order to frame my shots. My concern is what settings would I use to get an approximation of framing as close as possible to what my end result will be. Will using the 35mm setting on the viewfinder give me a close enoug aspect ratio for framing purposes. I know the Director's viewfinders are dead on, but I just need to know if this is a good investment tool. Since I am working with a very minimal budget, I am looking at purchasing the Opteka Micro Professional Director's Viewfinder with 11x Zoom. Can someone tell me if this will be an effective enough for my independent purposes?