The mixer you linked me is actually 4 way mono input and 1 mono output, but I really like the idea. Except apparently every mixer out on amazon has insane degradation or faulty hardware so I don't know where to start. But I really like the idea of plugging the outs of my focusrite into a mixer.
No - that's a headphone amplifier. 1 stereo TRS in and 4 sets of stereo headphones out.
I confused you by adding the bit about the little mixer, which you don't need unless you're headphone jamming with others.