The other system you can still run your start battery flat, yes you can manually switch on the other battery if you want.
The one I have shown you, you never need to switch, it is close to impossible to run your start battery flat as it will mostly never go below 12.7v except when starting.
If you want manual, get the cheaper system, if you want automatic get the more expensive system. If you are only ever going to install it once and money is no object get the better system.