We had 2 of these when we went this year, and will be buying them again when we go back.
We definately got our monies worth and our girls were only 3 and 2 at the time.
We ate in NBA, Nascar, Macdonalds as well as a few others i cant remember and the cards paid for themselves - We paid £10 each from floridatix i believe.
The only "restriction" we came accross was in NBA - you had to order an actual Entree for - not a burger or a sandwich - My HUsband wanted a Philly cheesesteak which wasnt an "entree" and we paid the extra $2 to make it up to the value of the cheapest "Entree".
If your littlun is happy to eat of your plate and your happy to share on occasion the majority of your dinner then its not worth it.
I like to order my food without thinking about whether its suitable for a 3 year old to eat. I like spicy food, and sauces on things which my girls just wouldnt want to eat.
We think they are worth it, but shop around because you can definately get them cheaper than $20.00