This looks like a combiner to me. Don't figure how this would do away
with a battery switch, which is for the output of the batteries. please
explain application.

I think the blue-sea Battery Link ACR equivalent available in West
Marine is $25 cheaper. It has a feature where it waits 30 seconds
before making a connection, has a manual control option, etc.

http://www.bluesea.com/product.asp?Product_id=53476