RE: Brownouts....
Been flying Spektrum for 12 months, 2 x Dx6is, 1 x DX8, multiple BNF aircraft, helicopters, etc...
Never EVER had a problem.
Brownouts will occur with any RX - it is a battery / BEC issue, not an RX issue.
Feed your receiver the power it was designed for and you will never have a problem.
Its like having a dead battery in your car and blaming the Starter motor when the car won't start!