i particularly recommend a different card actually the one im gonna link you, and even if you dont want it i used this site and its pretty great.
http://www.oz3ds.net/product.php?id_product=133
idk what features your card or whatever has, but many flashcards are getting blocked on the 3ds for ds games but this one runs fine. you can put infinite games on it, and it allows cheats, and all kinds of other stuff not said. i particularly like that it has the games small banner image aside their name so its easy to see games instead of just a wall of text like most other flash cards.
note, altho the card supports online, NINTENDO has shut down all online ds servers, so nomatter what you cant play any game online. (however you can maybe play on simulated servers with friends, but thats a pain to set up)
best of all its dirt cheap. IGNORE that it says its 'on sale' for 10$. its ALWAYS on sale for 10$ (these sites use shady business practices and will ALWAYS say EVERYTHING is 'onsale' just so your more inclined to buy it before the sale ends, and most everything will also always say NEW as well. however its still fair prices and good service.) anyway, its sometimes on sale for 8$ or 5$ so look around online you might get it cheaper from someone personally selling you theirs.