The main thing is, you should determine if a drug works for you on your own observations. Everyone has a different biochemistry. Personally, I dont care to much for it, and there are better AI's to use.
This goes for most AI's, crushing your estrogen too much to increase testosterone is not a good thing. You need balance.
See a 50 year old who takes ATD will have different results since their test to estogen ratio is out of proportion due to the aging process.
For people who have normal test to estrogen ratios, AI's are really good standalone stacks. Low doses of AI's are the best for these people, if they were do a solo.
I read a study a while back comparing different dosages of letrozole on increasing testosterone. I dont remember the numbers, but the study showed that .25mg for instance was just as effective as a 1mg.
I conclude the best used for ATD would be for on cycle estrogen check, "older people,30+", and to get a dry look, however not for PCT use. There are better AI's than ATD for all the above purposes.
My final conclusions, take them as you will. Its my opinion, and everyone is titled to their own, no one here can claim to know anything 100% and yes not all research studies are conclusive, but they can give good insight to help understand your own observations from the compound.