When evaluating electric toothbrushes, prioritize vibration frequency, which should ideally range between 31,000 to 48,000 strokes per minute for sonic models to ensure effective plaque removal. Look for brush head bristles made of DuPont nylon with end-rounded processing to prevent gum recession. Additionally, ensure the device has a waterproof rating of at least IPX7, allowing it to be submerged in water, and a battery life that supports at least 30 days of use on a single charge via USB-C or inductive charging.