This is almost totally ineffective either in changing the mind of your opponent or in convincing neutral observers. There are two main reasons for this failure.

You mention two reasons for this failure but neither of them seem to be remotely close to the most important reasons. Rational argument is, all else being equal, an abysmal persuasion technique. Is not this already well understood?

No one is legitimately entranced by a fallacy like No True Scotsman – it’s used strictly as rationalization, not as a faulty but appealing reason to create a belief.

I doubt that is true. I expect some people are persuaded by arguments of that form - and I believe I have seen people fall prey to just that tactic. It is also true in general that many (but not all) arguments are rationalisations.