These packs are NOT FOR SALE separately anywhere (stores could get sanctioning taken away if they sold them, see the Store Handbook for more information), and the Pokmon Leagues decided themselves how they were given out (League attendance, extra tournament prizing etc)
The Seal of Orichalcos grants the player a ton of power, some of which are: the ability to move monsters into the spell and trap zone that then can't be attacked until the front row is destroyed, the ability to summon more than 5 monsters at once, a buff to each monster on their side of the field that grans them 500 attack points, and The Seal of Orichalcos can't be destroyed by card effects, also the loser of the duel loses their soul
It's also important to note that this isn't specifically designed for the ranked meta, and while you can win and gain levels if you get lucky consistently, the deck isn't really built for climbing high in the ladder - though the YuGiOh Master Duel Six Samurai deck is good for this
In fact theyre so good I felt compelled to write this article