Sure, it has a drawback, but if your deck is built correctly, it shouldnt pose too much of a risk to your game plan
How to Determine the Converted Mana Cost of a Card In Magic: The Gathering With the exception of visual reminder cards, such as the Monarchy token or planeswalker emblems, all Magic cards have a converted mana cost, including tokens (whether creatures or not) and all lands
While duplicates can be beneficial for obtaining shinedust or flair cosmetics, they generally do not enhance your deck's effectiveness
According to the stories I've heard, Richard Garfield has kept these cards to this day, and no Chaos Orb version supposedly exists in these decks
A powerful card that works in the deck but not for the deck if that makes sense
If the target spell is an illegal target by the time Mana Drain tries to resolve, Mana Drain doesn't resolve