This is a "Backup Panel Installation" rather than a "Whole House
Backup".

This connection format is specific to Backup Panel (not Whole House).

Whole House has a lot of advantages, and one big disadvantage: if you
have any loads on your whole house which are not disciplined to turn
off during utility power outages (such as a Tesla car charging, or
electric heating and air conditioning units, or a pool heater), you
could quickly erase your backup available energy in the event of a
utility power outage in a way that you might consider to be
suboptimal.  If you are not home and come home after some time, you
could arrive to a possibly partially air conditioned home with
possibly partially charged cars with possibly spoiled food and no
electricity.  The advantage of the backup panel is that you can place
big loads on the non-backup panel to force the backup to not cover the
bigger loads you do not need during a backup.  Note that without
rewiring, that also means you cannot use big loads during backup
operation.

Advantages to Whole House Backup via the Tesla gateway:

1.  You do not need to derate the home load panel as mine was.  My
    internal panel was 200 amps, but when Tesla installed the
    PowerWalls, they derated it to 100 amps, and put the sticker on
    that said not to add loads. Since I intend to add loads in the
    future, that means I probably want to have Tesla rewire the
    Gateway to be a Whole House Backup.  I will let you know how this
    goes if it ever happens.
2.  You can charge your car.
3.  You can use all of your big loads, like air conditioner, heater,
    dryer, pool heater, etc., as needed, sparingly.

Given due consideration to the issues, I wish I had selected Whole
Home Backup.  We have temperate climate so not much need for
heater or air conditioning, so any of that we use gets used slowly.
I would be able to build an alert script that turns off car charging
in event of a power outage of more than a few minutes.

For other people, I would recommend Whole Home Backup if they get a
sufficient number of Powerwalls to keep them air conditioned, heated,
and car charging for a good portion of a few days, but also to try to
get a script built up to turn off car charging in event of a power
outage, so that you do not discharge your PowerWalls.  Also, an alert
to tell you when backup is on is a good idea so you can have the home
A/C and heaters turned down, and pool pumps turned off.