They can scale well if you know what you are doing in relation to the drive servos for the AZ and EL axes.
I am presently building a solar tracker using your LDR tracker array and your Shield board.
However I am using these amplified servos to drive the AZ and EL axes. The PWM drive signal comes from an Arduino Mega 2560, but the servo power comes from a +6vdc power supply.
I am using four Voltaic 6 watt solar panels that can be switched from 6 vdc up to 24 vdc depending on how I setup the four solar cells in series/parallel combinations. Therefore the current can vary from 4 amps at 6 vdc to one amp at 24 vdc.
The tracker frame including the solar panels weighs around three pounds which is easily handled by the amplified servos. The AZ base rides on a 12 in diameter ball bearing turn table to reduce the vertical load on the AZ amplified servo.
Front View showing four Voltaic 6vdc/1A solar panels and Brown Dog LDR tracker array
The Solar Tracker array is presently powered by a DC power supply, but will eventually be self powered by one set of the two sets of solar panels.
Still a work in progress!