FYI, I am the OP. I have since that post switched to Efani (from AT&T). Efani offers either AT&T or Verizon sims to use on said network.
The difference between AT&T/VZ and Efani is the service that Efani provides. It is basically the equivalent of concierge VIP customer service. In that no one can sim swap you because they know you on a more intimate level and require excessive steps of proving your identity to make account changes.
Basically it is the equivalent of a world where AT&T and Verizon got their $hit together and properly protected their customers.
There is also the added privacy benefit of being once removed from AT&T's database (see recent leak, etc).
I recommend them as a great combination with GrapheneOS for privacy and security.
And regarding the expense, it is not that much more that the equivalent AT&T plan (5G unlimited data).