I got one of those offers on my flight IAD-FRA last week also when my IFE wasn't working. They gave me the card and also a nice bottle of wine anyway. My choices were the same - e-500's (I don't fly UA domestic so have a lot of these already), 10% off a future flight (base fare only), $200 off a domestic ticket, or 9000 miles. I thought I noticed a caveat on the use of the miles, but since it was my only useable option I took it.