Yup it's real, yup it has sound, some games run at full speed, others are a little slow but close, majority of games are fully playable. Playing Garou on it right now
Get it here:
Roms have to be converted to .neo format with the built in converter application, you need to put all your (mame) neogeo roms, including bios in the same directory as the converter application, then run the application with -bios1.
Once all your games are converted, toss them all in the root dir of your SD card along with the neoDS.nds (patched if your cart requires it) and away you go.