My Chulane, Teller of Tales EDH deck focuses on repeatedly using EtB abilities, my Teneb, the Harvester EDH deck focuses on reanimating creatures, and my Sigarda, Host of Herons and Ghired, Conclave Exile EDH decks both typically generate plenty of tokens, so I believe that I can keep Aura Shards in those decks, but my Jenara, Ashura of war EDH deck and Marath, Will of the Wild *f-etch* EDH deck do not typically have creatures entering the battlefield frequently, so I believe that I could replace that card in those decks, perhaps with a creature that has synergy with +1/+1 counters, since both of those decks have a strong focus on +1/+1 counters, and either Hopeful Initiate or Steelbane Hydra seem to be excellent choices for those decks, although there could be other very nice cards, as well
With all that lifelink running around, youre not going to mind paying two life for a card if someone wipes out your battlefield
Most commons and lower-rarity cards are inexpensive
A 65-business-day estimate, for example, translates to roughly four months of calendar time