Metal cards are relatively recent additions to the Pokemon TCG, as cardboard remains the standard for most printings
Misty remains a staple in the collector's market, as her popularity and collection of great artworks continue to this day
To make a closed system that will prevent getting dirt on cards, you have to put your collectibles into another layer of protection - this is the outer sleeve
It does look like a low-curve aggro deck is a thing in this format too, especially in RW, so I can see this being a nice fit there
Leovold was banned a few years ago because it created undesirable game states by easily locking other players out of the game. These cards are doing the same thing Leovold did easily
It fills up your graveyard with creatures and flashback spells, while simultaneously giving you the lands that you need to cast your flashback spells