Personally I've switched to the R4-3DS, cheap and does the job well on DSi and DS. Never actually used it on a 3DS though as I don't have one.
Piece of piss to put the firmware on. Drag and drop NDS 'backup' games. :http://www.r4i-sdhc.com/downloade.asp
Note though that they have release a "V4.5" to cope with the new "N3DS 4.5.0-10" firmware and are yet to support this on older 3DS. i.e. make sure you get a "v4.5" card!