I've been watching these for a while, but when I heard it had Dingux ported to it, I had to get one for myself.
It's a bit trashy out of the box, the screen isn't used properly, and the GBA emulator is slow. But if you load Dingux on it (which you can do from the internal OR external SD card), it's a whole new device, more like a GCW Zero than the cheap knockoff handheld it was. The mod is somewhat wonky but not difficult.
Here's where I got mine for $60, with free Amazon overnight shipping but if you don't mind waiting you can get it for less from Chinese sellers.
These emulators seem to run well, from what I've tested. There are others as well:
Atari 8-bit (incl 5200)
Sega Master System
Final Burn Alpha
Sega 32X and Sony Playstation have emulators but they don't run well. There was an Odyssey 2 emulator on native Dingoo, not sure if someone made a Dingux build, but that should run well too.