hans, its hard to tell if its a good unit, but just like surplus amps i make assumptions about their quality based on the brand, model no., build quality, and unique features. kung sa brand, hanap ko yung hi-end division like sony ES, onkyo integra, pioneer elite/exclusive, kenwood trio, etc. may nakita akong sony 333ES na match sana sa amp ko na 333ES din pero sayang ang engots ko hinde ko pa binili. syempre kahit na maganda yung modelo, may risk pa rin sa actual condition ng unit, baka may tama na. basta mababa lang ang risk (a.k.a. presyo), okey na rin sa akin.