I have the 4-12x40AO 1/2 Mildot.
Its nice, not amazing but certainly not rubbish for the money. It fits fine on a S400 with low Sportsmatch mounts.
The ret is lovely and crisp, I've not used it for bracketing, the mildots seem to be true @ 9.5 mag ish. It does have a very wide field of view, a bit blurry at the edges, nice in the ret area.
If you get the sunshade, prepare for a battle to get the dress ring off the scope, it was uber tight on mine and took a lot of persuading to remove to allow the sunshade to go on.
Can't see any reason to get the 3-9x40 over the 4-12x40.
The flip ups aren't the best, but they were free! The front one is too big if you put the sunshade on though.