What’s especially good about this card is that you can play it during an opponent’s end step and be able to attack with it during your turn, all the while getting any enter the battlefield abilities. Combined with other cards, it can actually set off some interesting combos. In any case, that creature goes back to your hand at the end of your next end step, so you still get to keep it as long as it doesn’t die or isn’t exiled before then.
Aethermage’s Touch can allow you to toss an otherwise much more expensive creature onto the battlefield. If you find ways to reuse this card or its effect, it can be pretty valuable. The best way to abuse Aethermage’s Touch is to be able to “blink” the creature that is summoned with its effect, meaning to remove it from play and have it return to play at the end step with a card like Conjurer’s Closet or the effect of Venser, the Sojourner or Nephalia Smuggler.
The card actually saw a bit of play during Ravnica Block constructed when Momentary Blink was in Standard, which doesn’t even wait until the End Step. So if you summon the right creature with Aethermage’s Touch, it can provide a ton of value if combined with “blink” cards. Used correctly, it’s a sweet little combo trick, but not quite as sweet in Commander as it was in its Standard heyday.