We are using this BO successfully since Jan 2017. This BO is not designed to win every game. It is designed to win 60% to 70% of your games, which is enough to get promoted.
Mamba is a Zerg-GM, who won his first WCS points in 2017. See quote below.
Mamba (Swiss player)
2017 Mamba participated in the global event of WCS 2017, IEM Season XI - World Championship and won his first WCS-points.
The Build Order (Patch 3.x)