my friend has one of those, my better concience keeps me from getting one. once you buy one you dont have to buy games anymore, you can just download the roms for any supported games, including ds games. when pokemon diamond/pearl came out, my friend just downloaded his. i paid for mine...
I dont think the R4 can play any games other than DS/DS homebrew games. I own one and i have never tried it but i would like mor info on this as i dont think it is possible.