I got the $5 credit with purchase/sending of $50 gift card (by text) as well, but I didn't post it since it looked to be a targeted offer. As others have done, I sent the gift card to myself, and it was easy to redeem.
I actually spend enough at Amazon that I'm happy to get $5 of credit for spending money I would spend anyway.
Hard to believe, but I do actually buy things other than e-books
from Amazon, mostly stuff for our house, as well as some special no-scent products for one of our family members with skin sensitivity, so using the $50 is not a problem. And getting $5 credit for ebooks for it is all goodness then to me...