Well, it's true that the build quality isn't up to par with big names like Apple, Microsoft, Sony and Nintendo.
The thing is, compared to all the other cheap PMPs you've shown interest in; the A320 beats them hands down. I believe that's the consensus, anyway. Even if some other cheap PMP had better build quality, they still don't have the great homebrew community that the A320 has.
Even if you end up getting a dud A320, just send it back for a new one. I'm sure http://www.dingoo-digital-usa.com/
will be happy to see you get a good working A320. He's seems like a good, sincere guy.
Your best other option would be to wait to see how the new Gemei A330 turns out.
Or you could go for the GPH Wiz/Caanoo. But that's like, twice the price. Not really cheap.
Or you could go for the supposed king, the Pandora. But that's OUT OF THE QUESTION, price wise.