It's impossible to say without the thing in your hands, and even a schematic would help, but it looks pretty damn good to me. Looks like the opamps are socketed so you could easy change them for LM4562s if you wanted a known audio opamp, although the MC33078 is probably OK, if you google it you'll get the datasheet, I did.
I read 15V on the transformer, that's 21+ peak, it should mean plenty of output swing (looks like 2 regulators, probably +/-18V) to drive even the most difficult of phones.
$61, shipped, for the assembled board. Damn. It's hard to compete with prices like that, you'd be hard put to just buy the parts for that.
Looks like the front panel on the assembled one is a solid chunk of aluminium and the whole case is made from ali plates and right-angle extrusions.
4 O/P devices PC, complementary push-pull, 'course it's all down to the implementation, but there's the makings of something really good there.