I have almost exclusively used Frontline and frontline plus since it came out about 20 yrs ago. I switched to advantage one year but when back to frontline. I prefer the spray on formula. That said, I haven't had more than one flea in years. I treated dogs and yard and house when we moved here, treated the dogs every 3 mos. The next year, the next year, then I realized I hadn't SEEN any fleas the last year. So I treated the dogs in April and then in Oct as a preventative. Did that for a few years but never saw another flea unless I brought in a rescue. I keep a flea comb and check them often but they think it's just to annoy them as there are never fleas. So Frontline helped me kill those in my environment and they haven't moved back in. Oh except when they cleared a huge area near me and we got fleas, mice, possums…. sigh. But that was only that one summer, none since.