I have tried bow mounted range finders in the past and wasn’t very happy with them.  The Leuopold Vendetta proved itself to be a winner.  Make sure you read through the instructions and understand them completely because the set up is very important.  I went online and watched a couple of videos on how to set it up just to make sure I did it right.  It’s best to wait till 30 minutes before sunset that way the laser shows up better.  Basically what you are trying to do is align the rangefinder parallel to your 20 yard pin.  This allows you to range targets at full draw.  You simply draw and anchor then put your 20 yard pin on the target press the bow handle mounted trigger and it gives you the yardage on a large display.  That has always been the drawback to any rangefinder.  Deer are constantly moving and usually by the time you range him and draw your bow they move.  With the Vendetta you range him and shoot.  I used it on a deer at 22 yards and one at 42 yards.  I would highly recommend this product.