My understanding is that the box squat helps develop the lower portion of the squat as well as explosiveness because you can't take advantage of the bounce.
My gym doesn't have any boxes or anything that approximates a box (and I've asked if I could make one and 'donate' it.. no). The benches aren't low enough for me to be useful.
However, if I place the bar on the lowest (ie the flat) part the squat rack, it's about hip height. If I squat under that, I'm literally Ass-to-Grass, maybe a little lower (I feel the stretch).
Is starting from that position and exploding up a good proxy for using a box, or is there something inherently beneficial from the starting position sitting on a flat surface (ie box)?
Maybe I'll try to get a pic tomorrow.