I'm terrified of all the flea sprays out there making my cats sick. My family once purchased an $80 spray direct from the vet and it didn't work at all so I don't trust the expensive ones either. I'm also suspicious of some of the "all natural" ones because some of them use ingredients that I have read are poisonous to cats so there doesn't seem to be much oversight with the holistic products. I decided to try this one though after seeing it on Jackson Galaxy's website. I sprayed it on some fleas directly and while it takes a moment or two, it does kill them. The bottle goes farther than I thought it would too. I was able to spray my cats several times each over a period of weeks before it ran out. None of my cats got sick or got those "startle" responses. They didn't run from me when I went to spray them after the first time. I even used my hands directly to rub into their little cheeks and chins, got it all over my hands and I had no bad reaction even if I didn't wash my hands immediately. It doesn't really have a smell either, which is a bonus. I plan on continuing to use this.