As far as I am aware, the Curse Voice client has simply taken the place of the launcher 2.0, and, presumably it's taken over the release date of Soon (The one copyrighted by Valve). It is supposed to more feature-ful, but it is worth noting that it is also intended to be a part of a greater whole. The MC launching function is not going to be the "main" function of the client, as it also serves a number of other games. It should, however, be reasonable enough to get used.