The higher end ones are "quad core", sure, but it's important to bear in mind these are Cortex a5 cores. Not even the old A9s, A5s are smaller, cheaper, slower. It's would be like advertising an octacore computer, but the cores are Atom.
I'd still be interested to see some benchmarks, can't find any on the A5 especially in quad configuration.
At these prices, they should be able to break into the market, but the saying "You get what you pay for" is probably true.
Running stock Android, they should give a much software better experience than all the big manufacturers (except Motorola.) I do have an issue with Archos though as I have yet to get a well built reliable product from them.
The reviews of all their hardware on Amazon are fairly similar to my experiences with their android and windows devices: not charging, feeling cheap, locking up, random pause/stuttering issues etc..
This is a company that almost always fails in what they do. Nice specs(though very dated), good price.. but its Archos, promise the world, deliver maybe a third. Ive had nothing but issues with some of their past hardware that I just shake my head when I see this.