Seconding. Having to remember a manual switch to connect or disconnect will be a point of human failure.
/and I'm curious what the source of this DC-DC charger fad is, particularly in vehicle-borne systems. You already have a high capacity DC charger, why add a second one? I see the necessity in an off-grid home solar system. But in a vehicle that already has an alternator it seems like an added expense and source of failure, to me. And then to compound that with a manual switch doesn't seem to make much sense.