I love the Vortex Diamondback 4-12x40mm BDC. I have 3 of them and I'm about ready to get another one.
If your eye can't focus, they do have a fast focus eye piece that takes care of that. Out of the box mine was off. I have a cataract in my left eye and my right eye isn't exactly stellar. I cranked it about 3/4 of a turn and I was in perfect focus out to 300 yards. Once you get it set up at the range, it's game on. No AO or side focus to fiddle with. Start off on 4 power. If you need to crank up the magnification for a long shot, you can. I love the lack of "bells and whistles" The BDC is fantastic. Once you get it dialed in the clarity is fantastic! For the money you get some insanely clear glass with this scope!
Robert