On top of everything else (offensively) wrong with this excusing and rewriting of his history, this also isn't good advice.
While the principle of, "consider outside perspectives and challenges to things you think and believe" is good and fine, the specifics he presents are unlikely to be helpful.
One big issue is that he consistently frames the process he uses to test his beliefs not as challenging his thinking, but "verification." He "go[es] looking for credible outside objective verification." This is a bad strategy for challenging harmful, false, or misinformed beliefs, because for most such beliefs, if you are motivated to believe it, you can find what appears to be verification. He seems to realize this is an issue in the final tweet, and clarifies that he doesn't just mean finding people who agree with you. Unfortunately, he then compares the process he advises to "prepping for debate." But again, while when you are prepping for a debate, you will (or should) look to see what evidence your opponent will have, the point of doing so is not to change your mind. It's to figure out how to counter that evidence or argue why your position is still correct despite that evidence. Because when you are prepping for debate, you are prepping to make the strongest possible argument for your position. I don't want to say it is impossible for people to change their minds with this strategy, but especially for things that people are motivated to continue believing (y'know, like their "most sincere beliefs"), it seems like it could only end up reinforcing those beliefs, even if they are harmful, false, or misinformed.
Which leads to another problem: what is the goal, exactly, of testing your beliefs this way? What he is encouraging with his advice isn't focused on the effect the belief has on the believer, or those around them, but whether "it holds up." You can also see this with his focus on objective data. But again, this doesn't work. First, because a lot of sincere beliefs - whether harmful, neutral, or beneficial - aren't subject to being proved or disproved by objective data. Second, when people hold harmful, false, or misinformed beliefs, especially when they are in a cult, part of that belief sometimes is that the person/people they are believing *do* hold hard evidence that would change the world if it was revealed/believed! To give an Andy-specific example, Abbey has written about how she fully believed that she saw proof of Andy's magic powers with her own eyes.
And incidentally, with that idea that "If it's real, it holds up." What does holding up mean? In the context of his advice in this thread, it seems to mean, "if the belief is valid, you will continue to believe it after seeking verification and reviewing the arguments against those who oppose you." I do not like this claim, and I do not think it is helpful, especially in this context. Sometimes things are true, but people cease to believe them due to misinformation and/or abuse. See, e.g., conversion therapy. A manipulator can make you think that your previously held beliefs do not hold up, that they are not true. In fact, this is what a lot of cults do. There is nothing wrong with checking facts and beliefs against outside sources and being willing to change your mind. But this is not productive advice on how to do that.
Finally, and most importantly: that's not how cults work. (Nor, for that mater, is it generally how "sincere beliefs" work. See above re: motivated reasoning.) As Abbey and the Tea Blogger explain above, people follow cult leaders "down a rabbit hole" because they are manipulated into those beliefs. The abuse and manipulation that causes them to hold those beliefs is not subject to fact-checking by neutral, reasoned debate. Nor do people generally leave cults because they successfully fact-check the leader's "Truth" (and generally part of the cult is disrupting the cognitive functioning of its members to allow them to do that fact-checking and analysis). It's relevant that Andy's advice here focus purely on the veracity of beliefs, not about recognizing abuse or control or harm.
(And the fact that it is not good advice feels especially offensive because this framing essentially puts victims of cults at fault for their own abuse, for failing to properly fact check the extreme things they are manipulated into believing. Because although he mentions that some people with "Great World-Changing Reality-Shifting TRUTH" are looking for money or power, int this framing, those people aren't active abusers or manipulators. The false "Truth" just "comes from" them, and they "want" money or power, but they aren't doing anything. He didn't damage the people around him, "it" [the horrific rabbit hole he went down] did the damage. The most active agency he allows cult leaders and purveyors of misinformation is that they "spiral," that they are victims of their own mind.)