Unfortunately these aren't actually made by Sony, they are just badged Digifusion boxes.
As these are 'graded stock', they are almost certainly boxes which were faulty under warranty, and were returned for credit. Presumably they have been repaired, and sent back out at a lower price - however, I notice they specify only 3 months guarantee?, graded stock should have a full 12 months guarantee.
There are actually two different versions of this box, the early ones had severe problems with being noisey, and an over the air upgrade actually broke the boxes all together - requiring a manual return to the original software.
Presumably these boxes will be the first generation ones?, but will have had the software upgraded manually - which provides a permanent upgrade, where you can't revert to the earlier version.
The price though isn't really very good, you can get similar boxes (identical boxes?) for a similar or lower price, that aren't second hand.