All of the above and would add one more from my personal experiences with OW divers.
If I am diving with someone with a different configuration than mine, I would add that a good buddy knows their own gear well enough to demonstrate or explain to me their configuration. Before we get into the water, they should be able to demonstrate/explain in regards to their gear how to dump weight, where their dump valves and inflator buttons are located, how they will donate in a OOG situation, etc. I find this is especially true for newly certified divers, vacation divers, or divers diving unfamiliar gear like rental or borrowed gear.
I don't care what kind of a configuration you dive as long as you know why you dive it and how to dive it. Being a good buddy I have to understand your configuration so I can help if an issue arises during the dive. And if you can't explain how or why of your configuration before the dive, I'd rather call the dive.