Hmmm, mounting on that one seems cumbersome (electrical before
mechanical), and they don't seem to have current draw specs (like,
will it eventually discharge both your batteries while parked).  From
the photo of the bottom, it looks like they're using two
automotive-style relays in parallel...not sure it relays in parallel
is legit.

I'm a big fan of the Blue Sea products.  My van came with the SI-ACR
7610, and I'm very happy with it:

https://www.bluesea.com/products/7610/SI-ACR_Automatic_Charging_Relay_-_12_24V_DC_120A

Street price seems similar, allowing for the wiring.

Alex