I've been using my Discover It Miles for the 3% cashback, but that recently ended. I had planned on accepting one of the mail offers I keep getting for the Double Cash, but when Fidelity upgraded their offering, I decided to go that route instead (I already have accounts with them). They were nice enough to send an email offer for the $100 bonus and 0% purchases/BT for 12 months a couple of days before I planned to apply, so I took them up on that.
Applied and got the 7-10 day on Sunday. Today (4 days later), it showed up in the Fidelity app with a $17K SL.