It is OK with a single attack as it offers a reasonable 12 point swing and the potential to leave behind a decent board presence
In Commander, where mana values are generally higher, its even more important
This can discount some crazy creatures by quite a lot
Xenos Cunning Whenever a creature you control with a counter on it dies, draw a card
Card Name Mana Cost Type Legendary Creature Human Cleric Rarity Rare rules Text LifelinkWhenever you gain life, put a +1/+1 counter on Aerith Gainsborough.When Aerith Gainsborough dies, put X +1/+1 counters on each legendary creature you control, where X is the number of +1/+1 counters on Aerith Gainsborough
If you had an Alpha card with a base buy price of $25 and it was graded down to EX, you would receive $20 for the card, or 80%