If it's New in box it is guaranteed to be below firmware 9.2 which will allow you to use CFW,ROM loading,Homebrew,Mods,Custom Themes,etc...Im a little ignorant- why would it being new in box matter for that?
I'm not gonna try to bombard you with info just get the 3DS do some reading about rxTools you will be able to use any DS flashcard after installing a fix, however you won't need a flashcart for 3DS games.It will be new in box. Does that mean I should go with that or one of the cards you recommended?