Well, I've just checked aliexpress and there's a single result for it. So I guess it's right now reaching its end of life, so you can expect it to get even harder to find from now on.
With that said - and keep in mind I speak from experience with the A320, which is only slightly below the A330 - I would say the A330 is still very capable, and it would fit your needs for portability, at the very least.
As for emulation, it depends on which OS you will go with - Native or OpenDingux. Personally I prefer OpenDingux because it has a less rough interface than Native, and since it's Linux, there's also a lot of game ports you can stuff in there (Doom, Descent, Duke 3D, OpenTyrian, etc.... of course, depends if you care about these things).
For native, you will want to avoid the default emulators - they are at best "ok", but usually they are lacking in one or more aspects - performance, accuracy, configuration ability, poor UI, etc.
So, if you go with third-party emulators... I'm not sure how well the best non-default GBA emulator runs, because I've never tried. The default native emulator is not so good.
Genesis and NES are pretty good if you stick to the ones on lion_rsm's emulation pack.
SNES is mostly ok (again, with the one on lion_rsm's pack, and also PocketSNES) - SNES emulation is on the edge of what the hardware on the dingoo can deliver, so it's a bit demanding on the device, but the majority of games will run good enough to be playable. This remark also applies to SNES9x4D on OpenDingux, so I'm skipping that below.
Now for OpenDingux:
For GBA, just go with ReGBA. It's recommended you get the GBA Bios binary to use with it to improve emulation compatibility. Doing that, I've got it running everything I've thrown at it, and usually with pretty good performance.
For Genesis, PicoDrive. It just works perfectly.
For NES, FCEU320. Only complaint I have with it is sound quality, which is clearly inferior compared to native. I still prefer to endure it than to drop back to native. I just got used to it in the end.
For all of these, you can find the links in the wiki (link at the top). Some of them may have newer versions since the wiki is somewhat outdated, you may want to check the listings on http://dl.openhandhelds.org/
as well (most dingoo software are hosted there and it's where many of the links on the wiki will point to anyway).