Other than they will help bring in snakes that are hunting for food, which in turn could eat your eggs AND suffocate your chickens while trying to eat THEM.
LOL...this is such a fabrication! I am not sure who scared you into believing this but it is so untrue unless you are talking about Chicks! Really ...I don't mean pullet-size either, really baby chicks.
As for the eggs. Only a few snakes eat eggs and of those I highly doubt one would be waiting for the egg to come out of the chicken and the chicken to not have a full blown 'freak-out'. Chickens will not get near a snake and if one came in at night it would definitely be the mouse hunting kind. A snake knows what it can swallow and if one is big enough to swallow a grown chicken then I would suggest a smaller wire on your coop! LOL
This totally made me laugh. It is the perpetuation that a snake is bad! Snakes are a gardener's friend, and yes! Even Rattlesnakes are beneficial and outweigh any risks (minimal as they are).
Getting back to mice. Mice and grain go hand in hand. If you feed your chickens so there are no leftovers laying about then there will be a reduction in mouse population. If there is an excess of food then there will be an excess of mice.
You need to get yourself off of the idea of a poison. Nothing in this world has ever benefited from the use of poisons and if that were the case there would be no mice. Use poisons and I bet you have still have mice. Poisons (such as what are used for mice) can sit and wait until one day, long from now, you forget you used it in that area and or the mice drag it elsewhere. Mice take their food with them.
What you need is a Tin Cat. They are wonderful, they are clean, they work!
You don't even need to put food into them, and I have been using mine for over 5 years now! What a great investment for something under $20.
Other than that, please do not see this as me 'bashing' you Broke; I realize we all have our indoctrinations from good intentions; but nothing in the world will be benefited by poisons and nothing could be so cruel and destructive! I say, God forbid if a cat or dog should happen along a dead mouse full of these poisons.
Please take the time to read this article!
http://www.marvistavet.com/html/body_rat_poison.html
Please be careful. We are only here on this Earth to usher in a better way of life, not to embrace the old school thoughts and consumerisms.
It is time to get back to basics and rekindle the Natural Balance that is missing!
Blessings, :watering
Ron