vm-series with AWS GWLB

[gongya]

We are to deploy vm-series in AWS with GWLB. The docs says "

To ensure that the VM-Series firewall can inspect traffic that is routed between VPC attachments, you must enable appliance mode on the transit gateway VPC attachment for the security VPC containing the VM-Series firewall."
In my understanding, appliance mode is used to ensure the stickness to one firewall member for bidirectional traffic flow. If yes, does that mean the two members of the firewall are standalone, no cluster between them?
We deployed Checkpoint cluster in Azure with AZURE LB approach, the standby does not reply the LB Probe. So no need to enable appliance mode.

Anyone can clear this for me ?

thanks !!