I know this answer is long past when the question was posted but my answer may help another customer. I bought a "quick finder" nail trimmer and can confirm that the product does not work. You are better off having your vet or other professional teach you how to clip your dog's nails. I have a German Shepherd and his nails are black (and therefore no way can I view the quick) and I assumed this would be a wonderful product. It was a complete waste of time and money in my opinion, and cannot caution against it highly enough.
Hope this helps everyone out there.