The difference of FlyFun-100A and FlyFun-100A-OPTO:
FlyFun-100A (PN=80020650) has built-in BEC, while FlyFun-100A-OPTO (PN=80020660) hasn't.

Description:
Brand Name:HOBBYWING
Item Name:HOBBYWING FlyFun-100A-OPTO Brushless Speed Controller
Item NO.:80020660
Output: Continuous 100A, Burst 120A up to 10 seconds.
Input Voltage: 2-6 cells lithium battery or 5-18 cells NiCd/NiMh battery.
Refresh rate of the throttle signal: 50Hz to 432Hz.
Max Speed: 210000rpm for 2 Poles BLM, 70000rpm for 6 poles BLM, 35000rpm for 12 poles BLM.(BLM = BrushLess Motor)
Size: 83mm*31mm*14mm..
Weight: 73g.

Features
Safety arming feature: Regardless the throttle stick position, the motor will not spin after battery connected.
Throttle calibration funtion: Throttle range can be calibrated to be compatible with different transmitters.
User programmable.
Multiple program methods supported: transmitter stick,LED Program Card. Very easy to program the ESC at home or at the flying field.
Compatible with Lipo battery and NiCd/NiMH battery.
Internal timing can be changed to be suitable for different brushless motors.
Full protection: Low voltage cutoff protection / Over-heat protection / Throttle signal loss protection.
Extreme low resistance PCB is used at the power output section, the whole ESC has super current endurance capability.
Microprocessor uses separate voltage regulator IC, with good anti-jamming capability.