So there's quite a few of these machines out there (the GP machines, the Dingoo, and others). let's talk about 'em!
So I just got mine, a GP2X Wiz. my first impressions:
it's attractive. I like the black and red and silver color scheme. I was worried about the shape of the D-pad and fire buttons, with metallic trim, would be hard on my thumbs, but so far they've been comfortable.
the games it ships with are mostly pretty good, actually. All but one are in English (the one being an Implode clone in Korean); most make use of the touchscreen, which is pretty responsive.
But clearly, the most important feature is PCE emulation. I haven't played many games yet, but the biggest problems seem to be audio stuttering in the emulator, and the fact that the Wiz does not recognize High Capacity SD cards; it will only read the first 2 GB of any SD card you put in it. A typical CD holds 650 megabytes; do the math, and you'll realize your dream of carrying every TG16 game in your pocket cannot be realized (at least, as far as CDs are concerned.)
There are other emulators as well. Some of their menu systems can be pretty complicated (for example, the Atari XE emulator) and there is little interface consistency between emulators; ferinstance, most of them require you to press "menu" to get to the options menu, but one (alex) wants you to press L+R.
One nuisance I've encountered so far is that the "lock" function doesn't seem to work: the power switch is the kickstart type (pull down and hold to turn on or off) but in the other direction there is a 'lock'. I figured it would suspend all inputs, so you can shove it in your pocket; it doesn't. this basically means I must get a case for it that doesn't push the buttons when I shove it in my pocket, and in the meantime turn it off between playing sessions.
So far, it seems like a playable, but flawed, machine. I'll review it again once I've spent more time with it.