What are TTds cards?

Answer 1

DSTT is a very popular card compatible with SDHC cards. Recently, the DSTT has fallen to the same problem as the R4: clones have found their way into the market. Many manufacturers are making cards that imitate the package and look of the DSTT. Some clones change the name (ie: DSTT-ADV or CN-DSTT) but most label their product as DSTT even if they are not affiliated by real DSTT Team. There is now a lot of information on DSTT official website to identify fakes and clones. and even a guide to telling if a DSTT is real or fake. Contrary to popular belief, running any unoriginal DSTT card does not "brick" a Nintendo DS. It is possible that the card itself will not work, but it does not affect hardware in any way. The most common problem with a legit DSTT card is the infamous "Menu?" screen, much like the dreaded R4 "Loading" screen, which is usually a software issue and can be easily fixed by installing the software from the DSTT website onto your micro SD card.

-Wikipedia