I have a Marbles on my Marlin in 38-55. The suckers are not repeatable. We shoot 100 and 200. You can't dial 'em up and back. I have my Marbles set so the post is on the bottom of the target at 100 and I hit the upper third of the target. I set the post on the top edge of the 200 yard target and I get it about dead center.
He would like to have one with good windage and marked yardage.
I will get him to check on the Brownell's sight.