I have the bushnell chuck adams addition with the Angle Range Compensator (or whatever Bushnell calls their inclinometer). Like others have said, on basically level ground the difference is going to be negligable. However, I have a couple of stand that sit on the side of a hill. and the different between line of sight distance and 'shooting' distance can be quite a bit. 15 feet off the ground, a 30 yard down hill shot can be as short as 25 yards on one of my stands. That 5 yards is the difference between a hit and a miss for sure.
Where it really comes in handy is on open ground that is hilly. No trees to range etc... I paid the extra few bucks and am perfectly happy with my decision.