I have a Shepherd on my 300 Win mag and another on my .22 rimfire. They work great and I believe they are the best hunting scopes. They are not target scopes. Not enough magnification and the crosshairs are too thick. I talked to the people at Shepherd and they said the thick crosshairs are to accomodate hunters in low light conditions, dusk and dawn when the animals are active. Optics are very clear and very bright. For a long time my Leupold 6.5 x 20 sat on a shelf while my rifles wore Shepherds.
I have 5 of them. One old Shootist 3X10, two P-2s, one P1A and one V1. The two P2s are mounted on a 35 Whelen and a 30-06. I have used them in conditions of low light both at dawn and at dusk. I can see both the animal and the reticle right up to the end of legal light. I will be mounting (re-mounting) the other three on another 30-06, and two 300winmags. I would have already done so, but I'm currently in Afghanistan and haven't been home long enough to get my reloading bench and rifle/pistol work area re-set up after moving to Colorado this Spring. One neat thing, though. I'm near Fort Carson, which has just built an extensive range complex outside Gate 20 and opened it to the public. And it has a 1000yd longrange rifle range as part of the complex.
You definitely need to work with them and understand how your setup fits in with the circles. My brother has owned one for several years on his .300 Win mag. I tried ranging with it on a fence, estimating the post height at 4'. I came up with an estimate of 1000 yards. Went to Google Earth and the measurement tool gave me 990 yards. Not bad! Glass does not seem to be as good as the Leupold on Dad's rifle, but on par with my Burris scopes, perhaps even my Nikon.
Got a friend that got one last year. He brought the scope and rifle (7mm)up for a long weekend of scouting, and banging the gong at long range. There was something tricky about the way he had to zero it, but once he did, he didn't have a problem banging the gong out to 1000 yards. It has circles in it, that is suppose to be used as a range finder on deer (I guess). This last year, he spotted a large muley buck, and he later told me the 6,7,8, and 900 yard circle all worked on the bucks chest, so he had no idea where to hold (left the rangefinder in camp). It cost him a dandy buck. He's learned to use the range finder, and not to rely on the circles in the scope. I thought it had decent glass, but not really sure how you would hold on a target at like 850? Probably have to shoot it a lot to figure it out?
It doesn't take a lot to figure it out. The circles are either 18" to match a whitetail chest or 24" for an elk chest if I recall correctly; you buy the scope accordingly. You can figure out the rest with a little quick, simple math. As far as the distances between circles, if one's too big and the other too small, they tell you to hold central between them. If you can tell it's a lot closer to one than the other, though, hold closer to that one. When it comes down to it, though, I think knowing a mil-dot reticle, front focal plane, and how your setup works on it is the better way to go. As a compromise, the Nikon BDC isn't bad once you figure out the subtensions of all the features at 100 yards. With that, you can do a decent amount of ranging, but again, know how your setup works with those circles. The one big advantage I see with Shepherd, though, is the dual reticle. If one moves, you will know it. As for sighting in with one shot as they claim, that can be accomplished on any scope as long as you have something to hold it steady while you adjust.