I've been using the Omega on my T/C Omega .50 cal. for about two months. I don't have the problem you're worried about. Just look right through them. The circles are hollow and the lines that make up the circumference are thin, so they don't cover up much of the target. Even though they're stacked fairly close to each other it was no problem for me. Can't blame a miss on a crowded reticle.
Nikon has a little movie on their site and it matches my limited experience so far. Choose the proper circle, look through it, press straight back and watch your target fall.
LittleWill