Sergeant's Pet Care Products review: Cat flea collar

Purchased this collar for our cats 1 is 1 yr the other 8 months old. Our 1 yr old has been sleeping a lot and not eating as usual nor has she been herself. Tonight upon arriving home my husband greeted the cats as usual to find what he thought was gum on her neck was actually a wound from her collar. We are treating it as necessary. Knowing what we know now we wouldn't have purchased it to begin with.