Your thoughts on a external UBEC with a dedicated battery

For my new to build HKH-500 I want to power the Rx/Servo's/Gyro independent of the ESC/motor.

First option:
ESC and external UBEC both connected to the same 6S Lipo. Like shown in Marc's video.

Second option:
ESC connected to 6S Lipo.
UBEC (includes lipo voltage monitor) connected to 2S 900mAh Lipo (which I still have some from my HBFP).
The advantage of this setup is that, if the 6S Lipo failes you can still autorate your heli to the ground (if you have mastered the manouvre ). Easy setting up the heli, no need to unplug the motor, just only power the Rx/Servo's/Gyro.

Is anyone flying a setup that resambles my second option?
Any estimation on how long (in minutes of flight time) a 2S 900mAh Lipo can power a typical 500-class control system (3 analog servo's on cyclic, digital tail servo and HH gyro)?

I wouldnt do it and here is why....To much extra weight and many others with this setup
have crashed because the RX lipo ran out of juice. Helis fly better light. Using an external
ubec is a great way to go. Anything can fail at any time so why not keep it light and simple...

I know Fatdaddy is using a seperate Rx battery so he can shed some light on how long they last. I really like just wiring in a seperate BEC myself, it always seemed like the easiest and safest route, but thats kinda because I'm lazy