Something is missing here. I know OPE prefers external BMS's over internal BMS's because all BMS are not alike. The old adage "you get what you pay for" seems particularly true with many of the off brand LFP batteries with an internal BMS. The criticism of these cheap LFPs has been the inability of the BMS on one battery being able to communicate with other batteries in the bank. This can lead to one BMS failure shutting down the whole system. With a single BMS for the whole system, this won't happen.
The most surprising part of the system was the inability to charge the Start/reserve battery or to easily switch the loads over to that battery. I'm curious about that. There are several ways to do that, with FETs, ACRs, and B2B chargers. I don't understand why the charging isn't happening automatically. I'll have to go back and look at some older Atticus videos, I'm sure he explains the system. He did record an interview with Nigel Calder before installing the system.
On my almost installed LFP system all charging will go to a charge bus. The Start/Reserve (AGM) will be charged by a B2B charger off the charge bus. Both the start and house batteries have separate on/off switches. Thus if all three LFP BMSs shut down, I'll still have the start/reserve battery for essential functions.