I have used the kit, and it seemed to stop the cracks from expanding, but alas, I didn't pass the state inspection later that year. Thankfully, in my state, regardless of your insurance deductible the most you pay is $100.
One of the things I liked about California was a strictly enforced covered load law. Here on the east coast, not so much, I have replaced my windshield 4 times in 10 years.