To people who are interested in DS Homebrew I've been recommending a Slot 1 flash cartridge called the R4DS. Watch what you buy, because fake R4DS units have been found in China and online.

These fake units have near-identical packaging and appearance to a legitimate R4DS. You can tell the two apart by the memory they use: a real R4DS will display a Micro SD logo on its packaging, and uses Micro SD cards. A fake R4DS has no such logo on its packaging, but has small blue stickers on the box and unit to show the amount of internal memory the fake has.

These fake units do not have the compatibility and quality of the real thing. Ask your seller before buying.