If you are using anything other than two starter batteries where an ACR would be more than adequate, especially a mixed chemistry like AGM or Lithium, then you have a very strong case to use a DC-DC charger.

I still feel there are better options to consider than the RedARC.

If you accidentally draw down the system killing both batteries, the RedARC solar charge controller won't be able to recover system because it needs 12v DC to function.

Personally I like having separates, especially when they provide more options and control, along with data and monitoring capability.

Even with the system completely dead the Victron MPPT would be able to recover and put charge back into the batteries. I use their DC-DC chargers too and together I find them to be a better option.

The Victron controller also has bluetooth for monitoring. You can see trending and live data for solar and battery monitoring. I like to nerd out on this stuff so I find it pretty useful. Also eliminates to need for a bunch of battery or voltage monitors.