I have been using these collars for just about a year and a half.  My one dog really really hated the drop type flea and tick.  i would put it on him and he would avoid me for days.  Whatever it was he really hated it.  So to that end i would not always give him the drops or i would forget.  He spends a lot of time out side and has had flea and tick issues in the past.  BUT not in the last 2 years that i have been using these collars.  He doesnt mind at all and has had no adverse reactions.