So my wife and I have done researched and talked and we are leaning towards the Seresto collar. I can't find much on adverse reactions to the Credelio, but I just don't want to chance him having a reaction to it. I like the topical and it has always done great, but it is messy and having to watch around the cat. I don't like the idea of giving my pets any pesticides but giving something topical seems better in my eyes than having him eat it. The collar seems to be the best route. Ticks and fleas are very bad in our area and we go camping and hiking frequently so he has to be protected with something. My vet has the collar and its around $80. Tractor Supply and Petco are about $58. I seen problems online about knockoffs. Are we safe to get them from places like tractor supply?