I have one on my 22-250. Honestly, I can tell a difference but only mess with it when I'm bored. I've never drawn on a yote or target and thought "dang, I'm out of parralax!" I could set it at 100yards and forget about it. You can tell a difference when you adjust it, but I've got a shotgun scope w/o AO and I've never missed it there. (I've shot 20-120yards)

Sooooo...all that to say this: It's not needed, but its a nice little feature. Only you can decide if its worth the extra $$$ and slightly more weight if you're one of those who concern yourself with how many ounces your gun weigh.