Dogs have been wearing Bayer's Seresto collar now for several years. No health/reaction issues with my boys. All my training group have been using them with total success. I leave them on while dogs are in the water and still seem to get good protection.
I like the idea of a single pill though but cost wise the seresto is a better buy for me. When I get south in the winter, they are the first things I order, hopefully they become available in Canada shortly.