I think that the article promotes two misunderstandings that would be easy to avoid.
The article is about human happiness and introduces the subject of study giving the wrong impression that Effective Altruism it’s only concerned about human beings, and also gives the wrong impression that GiveWell represents all Effective Altruism.
I think this is clear just reading the title: “A Happiness Manifesto: Why and How Effective Altruism Should Rethink its Approach to Maximising Human Welfare” and the abstract: “I argue effective altruists can and should use happiness surveys to determine cost-effectiveness and show how doing this generates some substantially different charity recommendations from those given by GiveWell.”
If there are doubts about that the article is only about human welfare, you can jump to this part, in the body:
″...(2) concerns about under- or overpopulation; (3) the meat eater problem, the impact saving lives has on increasing animal suffering due to meat consumption. (2) and (3) are important but too much a diversion to our discussion here on using LS measures...”
So, the article is about LS measures and other stuff and does not take into account the welfare of beings that are not humans (like other sentient beings classified as other animals species).
In the definitions of “effective altruism” there’s no mention to humans but “others”:
“Effective altruism is about answering one simple question: how can we use our resources to help others the most?” .
“Effective altruism is a philosophy and social movement that uses evidence and reasoning to determine the most effective ways to benefit others.” .
Maybe GiveWell it’s only focused on human beings , but it’s very confusing and unfair to identify “GiveWell” with “Effective altruism”. Effective Altruism is not only about human beings .
My first suggestion is to clarify that the article is about Human Welfare, without suggesting in the article that Effective Altruism it’s only focused on human beings.
The second misunderstandings that I think would be easy to avoid is:
Even if we focus only in humans beings, the article suggests that Human Welfare can be measured by surveys.
Unfortunately, there are some situations in human beings in which we can’t survey human beings, and those situations are linked with the most abominable cases of deepest and terrible intense suffering.
Sadly, we can’t easily survey (or we just can’t survey at all)  suffering in very young humans, humans in oppressive cultural situations, humans with some cognitive impairment, and humans who do not survive the experience of suffering. For instance, we can’t survey:
Suffering in fetuses, newborns and small kids.
Suffering in girls and woman in cultures where they are almost properties.
Suffering in young boys in some complicated family environments.
Rape in small kids (not easy to survey)
People being tortured and then killed.
Individuals with cognitive impairment or dementia (not easy to survey)
Individuals dying without palliative care.
Individuals who die drowned.
Individuals starved to death.
Individuals who die burned.
Individuals who die frozen.
Therefore, my second suggestion is to clarify that the article is about Human Welfare but restricted on experiences of human beings that can be surveyed, leaving out situations in which Human Welfare can’t be surveyed.
Or maybe the article works with the assumption that some kind of situations that can’t be surveyed may be extrapolated by other situations that can be surveyed. I think is necessary to clarify It.
It would be very nice to recognize in the article that precisely those situations that can’t be surveyed are linked with some of the most intensely undesirable situations.
Some of us (people who support Effective altruism) think it would be good to prioritize reducing extreme suffering, such as extreme suffering that can’t be surveyed, and this article is ignoring those situations giving the impression that they do not exist.
Why for free?