I read some forums where people recommended the flashcards in the link I gave. But if you say that DS flashcards will work with the latest firmware then that is good to know.I think at this point any DS flashcard that is sold as "new" should work in the latest version, as far as I know Nintendo gave up about the DS's flashcards.
Now, talking about quality, I don't remember quite well, but I guess that the ones from the link are kind of a copy of others, so, I don't know how the support might be.