Metal gears transmit more vibration and are slightly noisier. They also add 2g of weight compared to the plastic version.
** Included Horns:** The servo ships with a 4-point star horn (cross), a round horn, and a single-arm horn. The spline is a standard 21T, compatible with Futaba and many FrSky accessories. Emax Es08ma Ii Datasheet
While it performs best at 6V, ensure your BEC (Battery Eliminator Circuit) can handle the current. Some users suggest checking for stall current draw to avoid "brownouts" on power-hungry systems. Analog vs. Digital: Keep in mind that this is an Metal gears transmit more vibration and are slightly noisier