I sat on stage, side view, Row A, and thought it was great. It's raised and is level with the mezzanine. It's a skewed view and you do miss a little, without a doubt, but I really enjoyed the experience.
I can't say that i have sat in the onstage seating, but after seeing it from the orchestra I would be willing to bet that the show is 10x more enjoyable from there....there are some things that you definitely would miss from the onstage seating...but on the other hand i would probably want to try the onstage seating just for the experience...how did you get comps??
I sat in the back row and front row of on-stage seating. You pretty much have to lean forward the entire show in order to see anything. You're also looking downward at a steep angle.
I will say that it was worth it because of one scene. The scene is the father describing the bedtime ritual that he sees his son performing in front of the picture of a horse. Only from the on-stage seats do you get to see Radcliffe's facial expressions during the 'lashing' moments.