The $300 credit is actually a travel credit.
I've had it applied to bar/restaurant tabs, airport parking, and Uber rides.
Just pointing that out, since you probably want to balance that out with the credits from the Amex or other cards which may not be as flexible.
I can attest the same thing with AMEX. I paid a baggage fee (because I was too dumb to figure out to select 0 bags if you're military), and I've bought booze on the plane. Both were refunded by AMEX. Caveat: travel credit only applies to your selected airline (you designate one once per year if you like, in January), so beware of that fact.