NDS-Card is legitimate. Ordered my DSTT a few months ago. They do the whole email thing so they do not publicly post the email. Selling flash carts and accepting PayPal is problematic. Simply email them, they will send you the address, and you send the funds as goods to them. Still have PayPal protection, without them needing to declare the goods. You should get an email very quickly with confirmation.
EDIT: My mistake. You choose services, not goods. Still get PayPal buyer protection.
The email thing was setup because paypal bans paypal accounts related to flashcart sites.. So they setup a roundabout method to avoid getting banned.
Nds-card.com is actually the official sponsor of GBATemp. So they are both trusted, safe, and help support the Temp.