[2] The choice 1 (after the 4th move): The choice 2 (after the 4th move): This rule offers a good variety of playable variants in the openings that aren't playable by Yamaguchi opening rule like 13D, 13I, 12D, 10D.
After the white player puts the 4th move, the black player can put N alternative 5th moves anywhere on the board (instead of the default N=5 in the original Taraguchi rule).
[2] Compared to the default Taraguchi opening rule, this rule limits playable openings to those which don't have N winning 5th moves.
Taraguchi-N opening rule was accepted by the Renju International Federation (RIF) in 2011 in the General Assembly.
[3] This opening rule is official opening rule for Renju World Championship via Correspondence being held in 2012, European Championships since 2010 and some minor international tournaments.