When evaluating two-head electric shavers, prioritize independent floating heads that adapt to facial contours for a smooth shave. Ensure the motor speed is at least 7,000 to 9,000 RPM to prevent hair pulling. Look for IPX7 waterproof ratings, which allow for both wet and dry use and easy cleaning under running water. Additionally, verify the battery type; Lithium-ion (Li-ion) batteries are preferred over Ni-MH for faster charging (typically 1-2 hours) and longer run times (at least 60-90 minutes).