I bought one of those "Mystery Power Boxes" a while ago out of curiosity. The mystery item was a Legendary Treasures pack. The mystery card was an old foil Entei (Wizards Promo #34)... but it had a bunch of glue on the front, and not the type that just pulls off easily. I threw it away, but I've already got at least a dozen of these from similar repackaged blisters so it wasn't a big deal. The coins also both had glue on their backs, which came off easier but still annoying.
Both of the code cards were for Plasma Storm (also covered in glue). I don't remember which packs I got exactly, but they were all legit XY-era.
I haven't seen those tins in stores but I personally wouldn't take the risk with them.