you really don't know that your productivity increase is due to the particular techniques, and the nontestimonal evidence for the techniques is weak or nonexistent

I think that's too pessimistic. I have a pretty strong time-order self-report -- I spent many years being unproductive, implemented these changes, and then became productive, and haven't stopped yet. (Though the same is true for the weight loss from my diet change and addition of exercise...)

Not to mention, there is some "consensus of experts" here around these techniques, though admittedly this also doesn't mean much.

~

Expect your results not only to regress to the mean but also to be subject to the same yoyo effect as dieting. You are probably creating a long-term willpower deficit that will ultimately take its toll.

You could be right, but I don't know what basis you're making this from. Is it your personal experience? Do you have nontestimonial evidence that these techniques won't create sustainable change, at least for me? I think it goes both ways here.