The 3 dots is because of it being for a cross bow, and shorter shots involved, I bought it used too and never saw a red dot scope before and didn't know how many dots there should be....live and learn. I havn't tried the really long shot yet to see if at 100 yards one of the lower dots would be the one to use. At 25 to 60 yards the top dot is accurate.
As for being uncomfortable, not at all, after shooting hundreds of slugs allready, and 40 at once all in a row, I have not felt any sore spots or thought this does not feel right. It sits right into my shoulder very well.