I haven't heard of Discover giving an evap line. I think Kathryn (Astrolady) used these tests when she was TTC and swears by them, (Kathryn correct me if I am wrong and sorry if i am )

It defintiley sounds promising for you. As Tegan has said maybe test in another couple of days and see if the line becomes stronger. Good luck, I really hope you are announcing a BFP soon.