Some people here have used it. All it does it test for the presence of glucose in the urine, which all diabetic cats have. Since glucose builds up in urine until the cat pees, the reading will almost always be high. Blood glucose testing is a more accurate way of knowing that your cat's level is right at that very moment.
You can buy KetoDiastix at the Human pharmacy to test urine glucose as well, plus the strips test for ketones.