I have owned a few Nikon Prostaff scopes with the BDC reticle. In thier price range the nikon is really hard to beat and while I generally run leupold scopes on all my rifles I have found when looking for a cheaper scope there isn't anything that compares to nikon glass in the sub 200 dollar range.
I first used a 3-9x50 with BDC on an encore 30/06 barrel. The circles worked out extremely well with a 165gr load. Considering the circles are 2moa it is pretty easy to use them as a range finding tool. I used them to check range estimation figuring that at 300 yards the circle would be 6" in daimeter, just over two circels deep was about right the the size of a whitetails chest. I used it on three whitetails that year at 90, 300, 360 yards. All first shot solid hits.
Recently I picked up a 3-9x40 prostaff to put on a marlin XT17 in 17 HMR. The BDC worked out very well with the 20gr Hornady XTP load that I have been shooting. The reticle allows easily to shoot at extended ranges even with the rainbow like trajectory of the 17 HMR. Hitting a 20oz pop bottle out to 300 yards is fairly easy.
The "spot On" Iphon App was very easy to use and not only did it have almost all factory loads it has the option of custom loadings. It not only allows you to adjust the zero to most effectively use the circle spacing to take the maximum advantage of the reticle it also has a pretty good ballistic calculator on it along with the ability to print field cards. For a $4 app it is an excellent buy.
here is a screen shot of the spot on progam with my 17 HMR dialed in.