I've used it before:
Benefits.., if you have kids old enough to be on their own, it's really nice to be able to give them the vouchers. It's nice to have some of the food expense paid ahead of time; it helped me a lot in budgeting. When we used it, I noticed I felt less uptight about the prices.
Negatives: You don't get change back.., so you find yourself always trying to do the math and have them add in an extra pop or cookie at each place. We were there for 7 days, we bought the 5 day package, we still overspent. On the last day we did have fun with "random acts of kindness" just picking out people in line to give the vouchers to.., and that was after we bought like 20 lollipops to give out as souvenirs. This means we paid about $200 more than we needed to. (But yes, we are very 'frugal' and maybe other families would have spent more.) I couldn't stand the "no change" thing, so I was constantly doing the math to go a little over and pay the difference or it felt like I was throwing $$ away. I was also very disapointed that we couldn't spend them at all disney locations.., no where in DTD takes them, (at least they didn't then), which we did know ahead of time.., but also, the shops on main street, like the candy shop, didn't take them either. That just made me mad.., they have lots of food there and it was directly a DL shop..,
Overall, I don't think they are worth the effort and we won't do it again..., allthough I didn't think it was a rip off or anything. I might pay ahead of time for a character breakfast or something, but not the Dining package. If you do it, make sure you downgrade. (Like if you'll be there for four days buy the package for 2 or 3.) Because even with my 'frugal' self, we ate at Ariel's grotto twice and Blue B once and we still have a lot of vouchers left over.
Most important, whatever you do, have fun!