As to the other, I think the practical difference MIGHT be something like this: "We" go to the magisterium or the consensus patrum or whatever. We expect to find an authoritative and reliable statement. "They" go to the Bible, and have no expectation of an authoritative interpretation, and see no need for one. Further they expect that since even councils can err, that nothing is reliable outside Scripture. So the Church becomes an association of like-minded people, and fissparates frequently.
We have a greater stress on koinonia and tghe benefits of a visible communion. They teach an invisible Church of those who have made an appropriate appeal to the mercy of God in Christ and, presumably, don't doubt critical things like, say, "blood atonement".
My guess is that either they must appeal to an inner "assurance" or say it's unknowable whether one is in the True Church or not. We say it's easy to tell if one is in the true Church, but harder to know if one is going to go to heaven after one dies.
It's a package, I'm thinking, based around the turning away from the very idea of a magisterium.
I guess one could say, if every one is his own pope, then who says who gets to run services on Sunday? That is, one's entire approachc to the "Ecclesial assembly" will be different. What we think looks like Balogna, or worse, to them. What they think looks like anarchy and a systematic denial of the possiblity of epistemological certainty.
How'm I doing?
