I don't own one, but I have used one in the past.
I only offer this because no one else has piped up on the subject. I don't have Shepherd Scope, but I have used one before mounted on a 300 W.M. I have only seen these scopes on big game rifles where the scopes functioned very well. I can't speak for the accuracy of the circles for small targets, but as far as quality of the scope, I thought it be very good.
The thing is, the location of each cross hair for a particular range is fine, up to about 400 yds or a little less, depending on the gun etc. Beyond that, assuming all other factors to be equal, like the B.C. etc., when shooting at a small target, like a PD, the atmospheric conditions from Standar Temp & Pressure (STP) to 4500 ft or so can be larger than PD's torso (horizontal that is) and can mean the difference between a hit or miss. At 500 yds, I calculated from using Shoot software, a difference of 4" from STP to an elevation of 4500 ft, 85 degrees and 25% RH, using a 223 50 gn Polymer tipped bullet.
I suggest you have a look at it a little as to how you intend to use the scope and perhaps talk to the Shepherd folks and maybe you can find out a little more as to variables. Then see if it can be set up for your intended shooting.