I use this App non stop when I am shooting and have grown to love it. It is essential during prep, where i used to have to crop my photos in photoshop after every scout. I can email the images or create PDFs, which include lens and location, immediately during the scout. I cant remember how I used to scout before I had this...
During a shoot it is also invaluable. I can show the crew or director the shot without having to guess if they are framing it with the viewfinder the same way that I intended. We can stand around and look the frame together and discuss before bringing in the real camera.
This app gets so much use its on the main dock of my phone.
featuredp about Artemis Director's Viewfinder, v6.4