My answer depends on what kind of golfer are you. Are you a weekend golfer? Are you a low handicap golfer? Do you play in lots of golf tournaments?
Slope is a great feature. Sometimes makes the difference between clubs that you would have normally not chosen for the distance given.
If you play in a lot of high level tournaments you will not be able to use this feature on your golf rangefinder. Make sure you are able to switch it off. Most have that feature and learn to use the device without the slope so you don't feel you are at a disadvantage in tournament play.
I answer YES, it is worth the extra money.
Happy shopping and good luck!