Depends how you define gimmick. What they do is give you the horizontal distance, which is what you want to hold your sight pin for (assuming excellent form cause form changes as you aim up/down will have uknown effects that mess up the hole theory of this).

However reality is for most treestand shots the difference is really under 2 yards. Is a 2 yard difference worth getting worked up over? Can you tell the difference in point of impact between 30 and 32 yards? If so, does it matter?

However out west in the moutnains shooting off cliffs, at longer distances it will matter. Line of sight could easy be well over 40 yards on a horizontal distance of 20 yards. This WILL make a difference.

At the height gets higher and the horizontal distance shorter, it makes more and more difference.