If you have the Amazon Prime card this becomes a 2.5% benefit, since the grocery purchase will give you 5x pts and at 1.5 cpp it's a 7.5% benefit versus the Amazon Prime card 5% benefit.
To make this worthwhile you would need to buy alot of gift cards.... Basically I am getting $2.50 for each $100 in gift cards I buy - I think I can get much higher returns focusing my effort elsewhere...