I use a *New* 3DS and it works pretty well. I use it mostly for NES, SNES, Genesis, GBC, GBA, DS, and 3DS. All of them work pretty well. Haven't experienced any slowdown on any of the emulators. Apparently it can also run certain N64 and PS1 games via RetroArch, but I haven't dabbled into that.
Really my only complaint is the dpad placement, after a while hand starts cramping, but everything else has been solid.