I have used it quite a bit in the P223 and Prostaff series. In my p223 3x32 it it set for 55gr 5.56 velocity. Zero at 200yds and first hash is 400 and second hash is 600 with 300 and 500 being bracketed. Elevation, temp, ammo differences aside I find it darn close.
With the variable power BDC scopes, you go to their web site. Plug in your ammo information (bullet weight, speed, even environmental data) and it gives you a chart showing calculated bullet drops at given ranges. It has many factory round to pick from or you can plug your custom ammo in.
You can even adjust for zeroing at different ranges. Such as, it shows you the different drops it you zero at 100 vs. 200 yards. Then once you find you preference you can print a chart for review in the field. For the tech savvy, they have a phone app that lets plug the environmental data in real time and get your adjusted drops.
I have played with it and once you get it dialed in I found to be quite accurate. I imagine with more practice, a range finder, and with very consistent ammo it would be even better.