I remember seeing this thread and finding it hilarious and bewildering. I wondered where Nightstalkers got those tiny cards. And then just yesterday someone gave me these as a gift...
It's a real product! This is from a company called "Super Impulse" and they have a line of "World's Smallest" toys. Looks like they have a fair bit of Hasbro products in their catalog, although they seem to be an independent company, so I guess they just get a lot of licenses for Hasbro stuff. This is amazing. It looks like since then, they've also done Ajani vs. Nicol Bolas. So I'll be picking that up.
As for the rules question, the packaging indicates, "Yes! Actually Works!" So we seem to have our answer. These cards actually work.
There are companies that make 45mm x 68mm sleeves for mini cards in European board games. That's way bigger than these cards, but the width of the sleeves is almost exactly the same as the length of these cards. So chop off the extra plastic and you have side-loading sleeves that fit these cards.
I'm not sure that they are legal in MTG tournaments
from the Magic: The Gathering Tournament Rules 3.3 Authorized Cards Players may use any Authorized Game Cards from Magic: The Gathering expansions, core sets, special sets, supplements, and promotional printings. Authorized Game Cards are cards that, unaltered, meet the following conditions:
• The card is genuine and published by Wizards of the Coast
• The card has a standard Magic back, is a double-faced card, or is a card that is part of a meld pair.
• The card does not have squared corners.
• The card is not a token card.
• The card is not damaged or modified in a way that might make it marked. • The card is otherwise legal for the tournament as defined by the format.