One of the central tenants of Scientology is that truth is “what’s true for you.”
Now that may sound like extreme relativism, but it’s not. It’s more of an extreme pragmatism. Their argument is that, if Scientology is true, then it should help people. It does help people, therefore, it must be true. Their only apologetic is doing it and seeing if it works for you.
As a counter example, I would point to chiropractic. Yes, there is some credible, scientific evidence that chiropractic treatment can provide temporary relief of certain types of pain. But that does not then, necessitate, that all their woo-woo about subluxations and the rest must also be true. Neither does it follow that, if chiropractic can temporarily relieve my lower back pain, then it must be able to cure my cancer.
And that, of course, leaves out the fact that while chiropractic does have credible scientific evidence behind it, Scientology doesn’t. Indeed, what little scientific evidence there is on the subject (all related to the efficacy of Dianetics) shows that it provides no benefit whatsoever and that, furthermore, the fundamental claim of Dianetics (namely, that all people possess perfect recall of everything that ever happens to them, even when drugged or unconscious) simply isn’t true.
It also completely ignores the fact that lots of Christians and Muslims and Buddhists and Jews and folks of every religious stripe will point to the beliefs and practices of their respective faiths as being tremendously helpful for them. I’ll put a hundred or a thousand evangelical alcoholics up who will swear on a stack of Bibles that only Jesus was able to get them off the sauce for every alcoholic that Scientology can put up that’s been genuinely cured by Dianetics. Clearly both Christianity and Scientology cannot both be true, but both help people.
So, long and short, Scientology, at least with regards to the “try it out” argument, fails both the coherence and correspondence tests. That argument is neither logically consistent, nor does it align with the evidence.