Why do you need UBEC?
The UBEC is a switch-mode DC regulator separated from ESC (ESC---Electronic Speed Controller for brushless/brushed motor), it will take high-voltage (5.5 to 26V) power from your battery pack and convert it to a consistent safe voltage for your receiver, gyro and servos.
For traditional speed controller with a built-in BEC, it will very likely have only a limited ability to supply power to your receiver and servos without overheating. If you are using a high-voltage battery pack or have heavy servo load, you should consult the ESC specifications to determine what the stated recommendations or limitations are. In general, if you are using a 4 cells lithium battery pack, or more than a 12 cells Nickel based battery pack, you should consider using an UBEC because in such a case the built-in BEC of the ESC can support only 2 servos, which means it is not suitable for RC helicopter and big aircraft.
Specifications:
Output: 5V/3A and 6V/3A Switchable
Ripple: <50mVp-p (@2A/12V)
Input: 5.5-26V (2 to 6 cells LiPo battery pack, 5 to 18 cells NiMH battery pack)
Size: L51 x W16.6 x H8.5 mm
Weight: 11.5 g