it has worked well for me, how it works fyi - it is a low level poison that gets in the bloodstream. when insects feed on flesh or blood from these animals, it poisons them. it doesnt work instantly and needs to be redosed in 10 days. i clean out all bedding and replace with bedding/tobacco mixture. when dosing it, try to keep it where the chicken wont groom often; and make sure it gets past the feathers and onto the skin.
again, i would not use this on chickens i plan to eat. and i do not eat the eggs from the chickens i use it on - you will have to research that end of it.