I bought two "Seresto" flea collars, one for my dog, one for my cat. Neither worked. We ended up infested with fleas.
Upon closer examination of the cans I noticed that, there was no registered trademark symbol by the name Seresto, and a number of other differences in these cans from the cans that collars came in the previous year. The previous year the collars had worked.
I believe this company is not selling genuine Seresto flea collars.