I know - I've read up on it too. The soresto ones were very expensive in Cyprus but they were more effective. I don't know of any of the digs having had a reaction to them though. However there the ticks came with really nasty diseases so it was finding a balance between effective tick control and preserving the dogs health. The ones I bought were the Scalibor ones which aren't as strong but still did the job but didn't last as long. What I did notice was when I first bought Sam home from the kennels he was at I took the tick collar off immediately. we were still in Cyprus then for two weeks and the ticks still did not bother him although we walked in the same areas as before. Before he had the collar on he'd pick up loads of the damn things even on a short walk. Kennels got the Seresto collar for him and apparently the ticks just fell off him! It was removed at my request for use on another dog before he was shipped to the uk. You'd have to question just how strong the chemical is to be that effective!