Lastly- and this is why I don't own one myself- shooting it eats limited resources better spent on pistols. The carry gun is used and toted much more often then any long gun, AR or otherwise. AR ammunition unfortunately isn't priced to reflect this.
If shooting and training ammo is limited by time , logistics,and other factors -the rifle takes a backseat role to the carry pistol,all else held equal.
Which begs the uncomfortable question of why even own one to begin with, if every round fired in an AR represents a lost chance to improve with the handgun which is far more likely to be used in a life and death event.