Among those who have recently purchased a DSTwo for their 3DS/XL there is an alarmingly high rate of product defects. You can see many posts on their forum about it not working properly (ie alex rider/card isn't detected, 3DS shoots an error on loadup, etc.) A reseller stepped forward yesterday and said that about 30% of the cards they received and tested did not work properly most of the time on the 3DS/XL (they work fine on DS.) I myself have been having this problem and since I bought it based on the recommendations here I figured I should warn prospective buyers here about it. The supercard team seems to be currently unconcerned/ignoring it, and hopefully getting the message out there will lead them to do something about it.
Keep in mind not all cards have this problem so if you have already ordered one it isn't the end of the world and odds are somewhat in your favor of it being fine.
Keep in mind not all cards have this problem so if you have already ordered one it isn't the end of the world and odds are somewhat in your favor of it being fine.