I used to use this (although not as my main movement) back in my early twenties when I dabbled in bodybuilding. It was one of my favourite machines (also really like the hammer strength seated row machine), and my upper chest was definitely at its fullest when I was using it.
Part of the reason I think it was so effective is because of the angle (the handles move inwards towards each other as you get to the top of the movement). This keeps tension on the chest at the top of the movement because of the force pushing outwards, which isn't there in a free weight version which only has vertical resistance from gravity.
Part of the reason I think it was so effective is because of the angle (the handles move inwards towards each other as you get to the top of the movement). This keeps tension on the chest at the top of the movement because of the force pushing outwards, which isn't there in a free weight version which only has vertical resistance from gravity.