Firts things first:
this thing have tons of power to drive even the biggests headphone you have!
Usually we never use it above 1/4 the knob.
The led meters are very useful and bright.
The backlight in all butons make it very easy to operate in a dark room.
Didn't use the "main in" so far so i have nothing to say about it.
It could be useful to someone but is an headphone amplifier, it should make individual mixes, so.....
Regarding construction, its really solid. The knobs for example, they dont have a cheap feel. A solid and stable rotation.
Did i mentioned already the buttons backlight? :)
Overall im really happy with this piece of equipment. I think i made a good choice.