I really like this kind of introduction; they let you get into what the authors consider the main reason for their products existence straight away - this is what they will spend most time on and other features will exist at these features expense.

It is also the best place to start evaluating how "complete" a solution is; particularly when faced with multiple choices.

It was a tutorial very similar to this one that led me to choose flow over typescript - I did the equivalent of setting the "user" in this example to null, flow would tell me it wouldn't work and typescript just happily compiled away. In short, this kind of quick evaluation led me to deduce typescript is JS with loose types sometimes (but you aren't sure where) so as not to be annoying and flow is JS with restrictive types everywhere (that may not get your indirect but correct logic) so as to provide the most guarantees.