Flanking gives 15% extra damage per rank on targets that are not facing you.
It is very effective on soul strike, making it a powerful
ability to throw against mobs that are not facing you.
As for the weapon spec, just like melee weapon specials, flanking does not buff the damage
Conclusion: it's kind of meh but it will have a niche use for group PvM
for improvised rotations
https://streamelements.com/se-9300510...