I don't think many people have to learn esperanto at school or for work, clearly it heavily biases towards people who are interested in learning languages and esperanto in particular. You have to be very careful while creating your samples to compensate for that I think.
>One of the studies Wikipedia cites claims that you can learn the grammar of Esperanto in ~5 hours, which is "impossible" for other languages. That instead screams to me that Esperanto is taught as a detached grammar course in early instruction, whereas other languages will tend to start with a phonological crash-course combined with basic phrase acquisition, instead spreading grammar out over several hundreds of hours of instruction.
That might be true but on the other hand imagine teaching English students a "detached" French grammar for instance. I think the students would give up within the hour, it's too dense and quirky to be palatable. If Esperanto's grammar is really simple and regular and can be integrated in 5 hours it's a good point in its favor.
We already know that language acquisition is going to be driven in large part by motivation on the learner's part, as well as competency on the teacher's part, and it's all too easy to construct a study that self-selects motivated students and competent teachers for Esperanto and unmotivated students and marginal teachers for other languages.
Another major question that's completely unanswered to me is the effect of pedagogy on teaching (and, perhaps to a lesser degree, to assessing competence in the learned language). One of the studies Wikipedia cites claims that you can learn the grammar of Esperanto in ~5 hours, which is "impossible" for other languages. That instead screams to me that Esperanto is taught as a detached grammar course in early instruction, whereas other languages will tend to start with a phonological crash-course combined with basic phrase acquisition, instead spreading grammar out over several hundreds of hours of instruction.