There is a dog who comes to the grooming shop that was always totally infested with fleas. Always had fleas, sometimes hundreds at a time. The owners claimed they used spot ons without any success. The dog has a Seresto collar now and hasn't had even one flea on him. So I'd say they're effective. They are waterproof, can even leave them on for baths but of the dog is regularly in water llike swimming daily, they don't last as long ( 5 months vs 8). I think it seems like a good alternative to spot ons and may be more effective, at least for now. IME spot ons are not nearly as effective as they used to be. And I think the companies know this too, which is why they have reformulated their old products and are coming out with new ones. The Seresto collar is made by Bayer, who makes Advantage and Advantix.
They make one for cats too, so I don't think that there's an issue in using them with cats in the house.