The ReakTsun training is part of the WingTsun, like it is taught within the EWTO. GM Prof. Kernspecht has designed those 24 elements (6 x 4) as qualitative successor of the 6 BlitzDefence programs. While the beginner learns in BD how to act offensive, it is for the advanced in RT about a defensive approach. Hereby the student learns to react also on closer range.
The distance is shorter and the moment of reaction later, that's why the body posses an important role here. ReakTsun operates at the border between the 'First Block' (between wrist en elbow) and the 'Second Block' (between elbow en shoulder) while BlitzDefence guards the cross-over toward the 'First Block'. ReakTsun is the second line of defense for the case that the first was passed somehow.
Also on this my Si-Fu Keith R. Kernspecht has developed a follow-up (for the TG's), the four 'Routines'. Those are mainly attached to Biu-Tze abilities and are forming the third and last line of defense WingTsun and is thus playing part at the border of the 'Second Block' (toward the body). To be able to learn ReakTsun some Chi-Sao qualities are inevitable, therefor it is part of SG 7 till 12.
The ReakTsun programs are already implemented within the NWTO trainings and the SG topics. So, it is here not about a choice for one or for the other, because ReakTsun is WingTsun. But there are still also specific RT group lessons in the SelfDefence class of the NWTO academy. Nevertheless forms ReakTsun a certain part of the overall WingTsun classes (just like the expansion BlitzDefence®).