Out of the 4 main Lightning skills, this one seems to be the least helpful. It provides little to no advantages for teams with high chakra users compared to other available options. For sword ninjas that work best with M.B, they have low chakra skills and would be better off with Intent of the Warrior. Lightning Enhancement provides better raw stat bonuses in the first 5 rounds for Lightning ninjas, and Anbu Assault Tactics offers great sustainability with a less impressive attack buff. It seems like there may be a misinterpretation of this skill or I am simply not understanding it correctly, but Heart Flux doesn't seem to serve a purpose on M.B. The crit and damage buff is just too weak.