Clear something up... What was recommended is you don't open the full package. The ones sealed like so are worth more money for selling/collecting. More so then the regular on a card English/Japanese tamagotchi ancestors.
There was also a recommendation you buy the same shell on a card, not the same container/package type because the value is much lower and ey are more common. The clock design is a favorite, but it's able to be found on a website like Ebay for a steal.