And yes, there is a "maybe" number 4 in my list, "Is it a cult", but I decided it doesn't belong alongside the other 3. It's not quite as fundamental.
You don't want to attend Mass even ONCE with a doubtful priest, or a priest not saying the Tridentine Mass.
But you COULD theoretically isolate yourself from the cult mentality, at least for occasional Mass attendance.
I suppose being a solidly "Trad" priest who sufficiently attacks Modernism and Vatican II would also be optional in this way -- you could survive just attending his valid Masses. This item obviously disqualifies the Indult. But what Indult priests aren't also doubtfully ordained by a Novus Ordo bishop? So it's kind of a non-issue.
I suppose it would be an issue for SSPX attendance. The priests say a valid Tridentine Mass and they are validly ordained. But so many of them don't speak out against Vatican II, or they try to warm us up to it. So they must be "yellow lighted" or caution given -- you can attend with caution.
I suppose I'll have to further develop this "checklist".