From a raw potential standpoint, the Washington Redskins were smart to stake a claim on Alexander. That isn’t to say that Alexander has through-the-roof potential. He’s not an explosive athlete. And his timed 4.60 speed (although John Keim noted that he could have ran faster, had he had a chance to train for it) is below the cornerback standard.
However, Alexander has unique traits that have led some cornerbacks to have success in the NFL. Cornerbacks don’t necessarily need to be blazing fast. There are other traits that Alexander has that bode well for him.