Apropos of anything else and comments on the relative merits, this needs a citation:
"It also cannot be abused and if a dose larger than about 20 grams is consumed, it will not provide any additional relief and only cause stomach discomfort."
I haven't seen any peer-reviewed literature talking about this particular aspect of kratom or mitragynine, but if you look at Erowid or the kratom subreddit you will find hundreds if not thousands of people saying the same thing. Anecdotal, I know, but still.
Anecdote: I had a far-too-large dose produce obvious precipitated withdrawal – intense sneezing, elevated body temperature, and nausea. It resolved in a few hours. The plant contains a mix of agonists and antagonists IIRC, and this seemed to be protective. I don't use the stuff anymore, but it certainly didn't ruin (or even really damage) my life.
"It also cannot be abused and if a dose larger than about 20 grams is consumed, it will not provide any additional relief and only cause stomach discomfort."