No, there is no savings. Its more a budgeting tool then anything else. We've used it on our last 2 trips. We've booked when we had money, and since we aren't good at saving money- it made sense for us to pre-pay for our meals. Buy prepaying it takes the stress of needing so much money while we are there.
Actually, if you dont use the plan carefully, you could end up loosing money! They do not give change for the vouchers. So, say you spent $4.75 on a snack, you would loose 25 cents on a $5 voucher. Because we are a family of 4, we never had that problem! We just make sure we are spending over the dollar amount and give a little cash to make up the balance. Unused vouchers can't not be refunded, so you have to make sure you use them all! The first time we had them we bought cookies for the trip home, with our last few dollars in vouchers. I recomend you buy less days worth of the plan then you trip is- so if you are going for 4-5 days, get the 3 day plan. That way if you aren't big eaters (we dont eat 3 full meals a day) or you want to eat in downtown disney you have that option and dont feel that you have to eat on site because you have to use your vouchers.