This is very economical and works very well - it kills all fleas.  I have purchased it about 6 times and I am always impressed with the performance.  Having said that, I have always had Great Danes with very short hair, but I recently got a Goldendoodle with very thick, curly, fur like a sheep.  I put the collar on him and it has killed MOST of the fleas.  He still has 6 or 8 a day that cluster right around his groin (which is far away from the collar).  I BELIEVE it is because the collar is not touching his neck because his fur is so thick.  Therefore 4 stars instead of 5.  I am contemplating shaving a channel in the hair on his neck so the collar will fit better, but that will look weird...