All I know is Duo teaches the "going to" future first (I think they call it a form of "ir+ infinitive"), and then the simple future later, as two separate levels, so you conjugate the ir part, and then the infinitive follows. I think the course is made that way so we can use the verb forms we already know, whereas the simple future gives us yet another set of verbs to have to learn.
So, when Duo puts a voy a + infinitive construction, that's what I give him. (I obey Master Duo when memory serves me.) ;-)
All the confusion in this thread is warranted. There is simply no reason to translate this as "will take" when it is CLEARLY going to take. We have plenty of things to trip us up while learning Spanish so why unnecessarily mix up these two methods of expressing the future.
For he or she:
Va a tomar= going to take
Tomará= will take