Garbonz, even on a single 12V panel, the MPPT will find the more efficient balance of voltage and current to maximize power because nominal 12V panels can have a higher functional voltage (e.g. 18V). It's true that very small power setups will benefit less in comparison to cost, but that's below about 150W. This is a 320W setup and there will be a noticeable difference versus a PWM.
In addition, this particular setup has the ability to get auxiliary power via a 24VDC power supply (transforming 110VAC external plug-in power). Given that this controller has auto-recognition for 24V or 12V, it can switchover to taking 24V input and run all the same 12V loads (and/or recharge the batteries) in the event they can't or don't want to use the PVs.