Primal Vigor doubles tokens and +1/+1 counters, but the benefit belongs to the whole table. Your opponents receive the same replacement effects you do. That makes it a powerful choice for a deck that can exploit it immediately, and a more complicated choice when opposing decks already have strong token or counter engines.
Avenger of Zendikar demonstrates the ceiling: more Plants enter, then later landfall triggers place more counters on them. A token-producing commander can also turn the enchantment into a large army in one turn. Having the follow-up ready matters because casting Vigor and passing may give an opponent the first substantial benefit from your five-mana investment.
Its counter ability is narrower than Doubling Season's. It increases +1/+1 counters placed on creatures, not loyalty counters on planeswalkers, poison counters on players, or every counter type in the game. Token creation is broader: Treasure, Food, and other noncreature tokens can be doubled as well. That can produce resources for opponents even if they are not playing a creature-token strategy.
Before including it, compare how quickly your deck can cash in the effect with what the rest of the table is likely to gain. It is particularly appealing as a setup-and-payoff turn, when you can cast Vigor and immediately create a substantial board. In slower games, keep removal or a clear combat plan available so the symmetrical benefit does not simply help an opposing engine reach its finish first.
