The Hobbywing X-Rotor series ESC are a good quality multirotor speed controller. They have a broad range of programming features combined with a linear throttle curve. The circuits and functions are optimized for multirotors, reliable and very fast respond time, it's a great choice for your drone.
OPTO means this ESC lacks the BEC Circuit, BEC circuit is to convert the battery's input voltage to 5V for powering the Receiver. Most of the expensive Flight Controllers (e.g. DJI NAZA) has a BEC unit included, so many players will use OPTO ESC to save money and less work load on the ESC. However, if your Flight Controller has NO BEC included, you will need to purchase an UBEC module (5V) to power up the RC Receiver.