I've used it twice and sadly, I must say, it is not convenient or money saving. We've used it as a bugeting tool. We often book months in advance, when we have a lump of money such as a bonus or tax refund. We buy the plan to ensure we dont spend all the money before the trip. We are HORRIBLE at saving money.
The plan might save a couple dollars, less then $5 on most plans. The vouchers take forever for the cm's to enter at the register. You dont get cash back on them. So, say you spent $4.50 and give them a $5 voucher, you are out the .50. So you feel forced to spend more and give them some cash with the voucher.
I think this trip we'll go with a couple gift cards. I can load them up with a few hundred dollars when we have the cash. I think they'll be able to process them quicker at the register, we'll still "save" our money for the trip, and we wont have to worry about the voucher values.