Energy gained on a critical hit is in addition to energy gained from the Critical Strikes attribute. Therefore, this skill increases energy return in two ways: it returns one point per critical hit, and it increases the likelihood of critical hits.
While the critical hit chance seems low at even the highest level, remember that the percentage is combined with your level in Critical Strikes and the critical rate from your weapon mastery.
Anomaly! This skill provides the energy bonus even if your critical hit was prevented by skills like Stoneflesh Aura.