pretty sure acekard 2 is compatible with the upcoming dsi, but don't quote me on that. Other than that I have friends that have R4s and they are just fine, I personally have an m3ds real but it's a tad more expensive.
Unless you are 100% sure of what you are getting, avoid the R4. One original - no more firmware updates so its going obsolete, 11 clones some OK some awful - very poor choice.
jesse158 - are you selling your own gear!! It is soooo disapointing to see people trying to scam people. No1 - this is not a REAL R4 so its one of the poor 12 others - yes now 12 as another fake tries to con people out of their cash. Why cant they call themselves something other than R4? - they are selling a cr*p product calling it a well known name and then laughing all the way to the bank. If you are sure of firmware, know that it will work - then fine, read all the poor people conned into thinking they were getting a top notch product but ended up with a nice lump of plastic on this forum alone. And this is not the only forum there are loads of others all saying the same = Avoid R4 there are far better solutions to be found
I personally have an M3Real, and so does my sister. I definetly recommend it as it is compatible with all games and all emulators I have tried. M3 also supports SDHC SD Cards. It is also still actively getting updates, and is currently at version 4.3a. I have Sega Master system, Genesis, NES, and SNES emulators and they are all perfect. I also have several homebrew games and about 30+ DS Games on it, with no problems at all. Definite high rate of scamming on R4s. I have no idea if dsi is compatible with it. Go M3! Hope This Helps!