I'd just caution buying gift cards unless you intend to use them quickly.
There have been a large number of chains just like Grill'd that have recently gone bust.
Eg: Italian restaurant chain Criniti's collapses into administration
Agree. The number of times you received/intend to use the offer is also a consideration as well as your risk appetite (pardon the pun).
I’ve received the offer on two cards. The small risk of losing $40 is preferable to me than stuffing myself with a heap of food and turning the meal into an unenjoyable experience. If I got the offer on 20 different cards then obviously buying $500 worth of gift cards is a totally different proposition.