I live in the south and fleas have become immune to Frontline and Advantage. Please don't waste your money on either!
I noticed advantage and the Advantage 2 not working down here 6 or so years ago. Then I made the switch to Frontline. Worked great for two years and then I started noticing the dogs still had fleas. I thought maybe I'd got a bad batch so bought more and same stort...Wasnt working!
Activyl is great. I prefer it over the others (even when they worked) because it doesn't have a funny smell and the spot you put it on isn't as oily.
I buy the large and use a small syringe to measure out the appropriate amount for my dogs weights. I also use it on cats. Never use activyl for ticks on your cats! It will kill them.
Anyway as of today 2/21/17 this product works and works well. It lasts a full month. One tip = don't wash your dog before using. It works with the oils on the skin. If you bathe your dog before applying it will not work as well. Wait at least 7 days after a bath to use.
I hope this helped! Just please be careful if you're measuring it our yourself and search online for the right amount for your dog/cat.