is the site wirefly a legit site to order sprint phones?

I just am wondering why they are dirt cheap. Are they used or something? I would like a new evo 3d and wirefly sells it with new contract for 49.99 which is 50 less then sprint online. Also does wirefly let you add a line to a pre-existing sprint plan. I would join my dads for the 9.99 a month extra or is wirefly only a new contract. sorry for all the confusing stuff but i really would like to know. Also how long it ships. Anything will help. Thanks.