From what I've heard, the hardware of the R4 supports only non-SDHC cards and the firmware may be unflashable. The updates for R4 are loaders, not firmware. The 4GB non-SDHC referred to on R4's site didn't work very well and was discontinued. 4GB and up is SDHC which does not work on R4.
DSTT with YSMenu is similar to R4, but it may not have all the same in game functions as cards like Acekard RPG, a CycloDS Evolution, or M3 Real.