Oh you gotta love the black and white perspectives on things ...
Tea tree oil is well researched for a multitude of things in several species. It's also one of the safest essential oils (one of three widely approved for use on babies).
For instance, it's been found to cure athletes foot (fungus) as well as lotrimin & friends. It has antibacterial and antiviral properties too.
And like any medicine, there are things it can't do, and chances of overdose, and side effects, and chances the animal is too stressed to deal with any medication. And aquariums are not very standard environments.
As for "helps heal" ... I mean really. That's such a vague statement. Removing the cooties that started the problem helps heal right?
While people are bashing API ... At least there exists research, and the research is consistent with what one would expect from other research on similar substances. Stress coat contains aloe, which has salicylic acid - an anti-inflammatory. Aspirin is synthetic salicylic acid. What does the competition have? Synthetic plastic like substances. The research in favor of Stress Coat is consistent with the effect of aloe in human studies. I think the claim for wound healing on that one is accurate.
I've sadly had a lot of bettas with fin rot over the years. Heavy duty mess have always been followed by rapid death. Careful use of melafix and stress coat have been followed by recovery.
I'm always astounded by the people who say "there's no research that this works" when they don't really look all that far for the research. Natural medicine is complex; it can cause as much harm as synthetic medicines and can fail just a frequently too.
I've had antibiotics fail across the board for fish - I'm not following that with a claim that erythromycin is worthless.
Sent from my iPhone with three hands tied behind my back.