The R4DS has proven itself to be a great card, but it does have a few issues.
I've owned my R4DS for about 3 months now....
Issue 1; problem with locking the microSD in it's slot. This manifests itself over a few days/weeks of use. The microSD may refuse to lock after a few cycles of removal and insertions This is a common problem with the R4DS.
Issue 2; Download play doesn't work on many games made by Nintendo......and possibly others publishers. Trial an error....
Issue 3; A couple games may not function properly....Castlevania: Portrait of Ruin may crash on you if you're not using a really fast microSD card, and Tony Hawk's Downhill Jam runs slow, but both games tend to have these problems on most flashcarts.
There is no way to know for sure that future flashcarts won't also have these issues too. But we can hope.
The M3 slot1 card is essentially the same as the R4. Keep that in mind.
Future flashcart abilities will be unknown until they are are released and fully tested by the community.
While I haven't actually tried to play either game in "issue 3", I can say that I've ran about 75 games in my R4DS and have had ZERO issues thus far.
Hope that helps ya!