There are a lot of low quality 30A ESC out there!

Don't buy a 30A multirotor ESC that doesn't meet all of these criteria! 

Highest efficiency 100% N-FET design.

Highest accuracy with Crystal Oscillator (Temperature won't affect the PWM operating range like other cheap ESC's).

No low voltage cut off, because any cut off in a multirotor = crash.

No over temp cut off, because any cut off in a multirotor = crash.

Super high refresh rate, no buffering of the input signal, resulting in more than 490Hz response rate.

16KHz motor frequency, giving fastest response of the motor, and quietest operation as well (no 8KHz squeal).

Super simple, foolproof operation! Nothing to program other than the throttle range.

ESC Specification
Cont Current: 30A
Burst Current: 35A
BEC Model: Linear mode
BEC Output: 5V3A
Li-ion/Li-poly :2-4s or Ni-MH/Ni-Cd:5-12s
Weight: 25g
Size: 42*24*7mm

Packet content: 
1x 30A ESC