The cats are free. You know you are going to have the expense of a vet bill with an exam, shots, deworming, spay/neuter and that's if the kitty is perfectly healthy. I always just get my cats from a shelter. These things are already done and I don't have to deal with "strangers". Have you considered this idea?
The only thing these people did wrong was to not Spay their Cat.. There are lots of unwanted kittens and puppies being born and "tossed away" every day, so yes at least these people are making an effort to get the kittens a home. As has been mentioned you would still need to have the kitten checked by aVet and get shots, de-worming and PLEASE neutering/spaying, if you get one of these kittens and money is a issue,check with your local Humane Society, they often will refer you to a clinic which offers discounted services for "rescued" animals. By entering Animal Shelter and your Zip-Code into "search" you can find shelters in your area where the animals have already been checked and treated by a Vet and you get all that at a deeply discounted rate.:-) Good luck getting your kitten!:-)