They have tied up with some hospitals and giving you vouchers. It doesn't mean they're awarding those vouchers at the free of cost. The respective hospital costs much money and they rejig in the vouchers. In this way, hospital and they are getting money. At the end of the day, you'll be the loser. Few things vex me are:
Delivery is time taking.
PIN CODE doesn't eligible, at most times.
Though they're genuine, costing multiple times of the original price.