Okay, I've been putting this thing through the paces tonight, testing everything I can think of. This is just my random thoughts and not really organized into a real review, so it will be TLDR probably.
So, I love this thing. Build quality is nice. Not as good as a real Nintendo system, but a step above most clone stuff, including my beloved GB Boy Colour clone. The D pad and buttons feel good and are larger than most handhelds, about the same as a regular PSP. It has a 6 button SNES style configuration, Y and X are just remaps of L and R. This is extremely handy in games that use L and R as action buttons such as Double Dragon Advance and Super SF2. The system lacks the ability to remap, however. The positioning of B and A usually bugs me (I would prefer it to be Y B, like Super Mario World on SNES) but I'm pretty okay with it here due to the angle of the buttons. I really hope this company uses this shell and buttons to make a Dingoo type emulator handheld. This thing would be sweet for SNES.
The screen is very nice. The specs say it's 640x480, but I'm pretty sure it's actually 320x240. You have three screen options: 1:1 pixel display that looks great but is a postage stamp size, full screen which stretches it slightly since it's a 4:3 screen, and a correct aspect ratio option which puts black bars at the top and bottom of the screen. Under correct aspect ratio mode, it is the exact same size as a GBA SP screen. Since it does upscale, it isn't quite as sharp as a real SP, although it looks better than playing GBA games on a 3DS or a Wii U. My preference between full screen and correct aspect ratio varied depending on the game I played. You see less upscaling artifacts in full screen, oddly, so that is my pick for text heavy games.
On audio, well, this is a GBA, so audio isn't its strong suit. That being said, this think kicks the shit out of a real GBA in audio. The sounds are all perfect, but the improvement comes in the quality of output. On the SP the internal speaker is pretty weak, and the audio is extremely noisy when using headphones. On the Revo, the the internal speaker is about what you'd expect but you can get it much, much louder than the SP. Too loud, actually, I kept it fairly low. It really shines with the headphone output. It's super clean, and strong enough that it actually powered my Sennheiser headphones that don't normally work well on portable devices.
It comes with a AV cable that connects the unit to a TV by composite. The cable is mono only, I have no idea if the unit is capable of stereo from the AV port if you used stereo cables instead. You could always use the headphone jack to get stereo. I hooked it up to the composite input of my PVM. The image was pretty great, although composite on my PVM isn't very good. The colors looked a little washed out (probably the PVMs fault, brighness too high in lowest setting) but it looked great. Supposedly the fullscreen output is 640x480, but I get scanlines so I think it's actually 240p. The image is a bit on the soft side. It fills the screen so there is a tad bit of vertical stretching, and you have the option of a smaller, sharper window instead, but no widescreen correct aspect ratio support. Compared to other GBA TV alternatives, it looks much better than my RetroAdvance GBA to SFC adapter. It's been a while since I used the GBA player, but I think it looks better than the GBA player through composite, although if you used homebrew to get 240p out of the Cube with component I'm sure that would destroy this. I no longer have a Cube component cable, so this thing is my new preferred method of playing GBA on a TV.
It comes with a little micro SD to GBA adapter for teh romz, and it works perfectly. The menu is a no bullshit text menu, and the roms load instantly. Mine oddly had a loose solder ball inside of it rattling around, but I opened it to get rid of it and all is well.
As far as the gameplay itself, it does seem like this is a hardware clone and not an emulator. Every game I played felt just right. The one exception I found was Super Mario World, which played perfectly but had a bug where solid blue backgrounds showed up as black. The one thing that did not work is my old Supercard flash cart. It's not at all necessary since the included adapter is superior, but I thought I'd try it out anyway.
The system has a built in emulator for NES, Gameboy, GBC, SMS/GG, and PC Engine. They're pretty terrible. If you've ever used the emulators on a regular GBA with a flash cart they aren't any better here. They may actually be worse. Gameboy black and white games played fine but some of the sound effects were off. NES games played fine but looked pretty bad. GBC and SMS played okay but was quite a bit slower than the real deal, and PC Engine was unplayable. I'm pretty sure most of these actually ran better on a real GBA, they sure don't use the extra speed of the Revo. I'll definitely be sticking to my old GB Boy Colour for regular Gameboy and GBC games.
So, to conclude, this thing is awesome. Just like the GB Boy Colour is my preferred method of playing GBC games, this thing is now my preferred method of playing GBA games. Also like the GB Boy there are some faults, namely the screen not matching the resolution of the source material and causing a little graphical weirdness.
If you have any questions, shoot. I normally wouldn't post a wall of text, but there aren't a whole lot of reviews for this thing out there from people who have been playing GBA since it was new and have used multiple versions of the hardware.