As I understand it, the neutrons only come out horizontally, in the cardinal directions, in the y-level of the centers of the toroid magnets. The reason some people stack up boilers like that is because (they think that) their reactors produce more heat than could be dealt with by one layer of boilers. If the boilers are stacked vertically, water and steam lines can just be attached to the top and bottom of the stack, which saves on pipes and steam lines.To answer the question "Would you build this?", yes, I am doing it right now.
One thing that I've been wondering about is whether the neutron emission takes place on only one Y-Level or on several Y-levels? I have recently seen a video of someone building multiple layers of boilers & neutron absorbers/reflectors and was wondering if this is actually worth the effort or not (400 boilers and 100 absorbers vs. a multiple of this do make a difference).
As for why the people that stack up boilers in their fusion reactors also stack up the neutronreflectors... I have no idea. Seems like the ideal thing would be to fill that space with something very good at conducting heat... but I don't know what that would be.