I've had one in the past for free but only tend to use them once or twice per trip.
If you will be eating at a lot of the places on the list then yes they will be worth it.
Most places on the list offer other coupons and offers. You can't use both these and a kids eat free card.
eg village inn we ate on a wednesday which gives you a free slice of dessert pie per person - saving of $12 dollars ish - so we paid for DD's meal which was about $4 instead of using the kids eat free.
My two dining in a budget reviews - links in my signature have lots of info re coupons and kids eat free nights eg mannys kids eat free mon and tuesday no card needed.