Worked great!
I had already bought a sizing kit from Walmart so I knew my size but came across this and wanted to try it. I did both hands using a black credit card and a white piece of paper. I did my right hand first, it was pretty quick, then did my left hand which took a bit longer, but both sized to a 9 which was exactly what I wore from the sizing kit on both hands! It does work but takes patience to turn the cross hairs green then hold still to take the picture.