The app appears to work fine. I used it on my 7D, 5D2, 5D3 and 1DX. However, since my 1DX is fairly new, I know the exact count from looking at my file name sequence. This app is underestimating by about 1000 shots. However, even the built in shutter count on the 1DX is not reading properly. My real file count is 4400, the app reports around 3500 and the 1DX menu shows <4000 so obviously even the internal count isn't right and that is what the program reads. However, as a general measure it seems to be fairly accurate probably reading the camera correctly but it seems the camera itself doesn't store the data accurately.