All 40 adult cats are on Program injections as its easier for us to control and catch the odd feral although a couple of the nice domestics can be worse - a couple of my handrears Cougar and Puma!
The dogs are also on Program tablets they get one a month
We have not had a flea issue since going on to this about 7 years ago. baby Beijing has been frontlined much to her horror and Ace, Cissy, Ragamuffin and Smudger have all be Profendered - Ace as we really have issues with him and he is a fighting boy at humans - I know to my cost and the other three have just come inside after 14 years and 8 years of living outside so they are in the humanisation stage but have adapted wonderfully!
Works for us in a multi household and we have no issues or reactions - Cats are aged 17 years young down to 10 months so a broad spectrum and no reaction from our Diabetic boy either