Hi,
If you use a BatShare your servo voltage will be approximately 0.3V to 0.45V lower than the battery voltage depending on current load. If you use the SportReg you need to keep it set at 5.5V as there is approximately a 1V drop-out voltage of the regulator. You need to determine your best setup based on your servos too. Personally, I would use the PowerExpander Sport Plus to protect my investment.