I have used a pair of 10x42 Diamondbacks for a few years now. I found several "blemished" pairs for sale on CameralandNY that only had some minor color issues externally so I could not pass up the super deal they had on them.
After using them and comparing them to a few other companies products I feel they are pretty decent middle of the road glass. I have compared them side by side with Nikons EDG's, Leicas, and Swaros. Myself and hunting partners agreed that the Diamondbacks were every bit as good as the EDG's but can't compare to either the Leicas or the Swaros. Using them at distances under a half mile with reasonable amount of light they fit the bill very nicely and provide a crisp, clear image. It becomes very apparant that they are cheaper glass when using them in low light conditions and at extreme distances when comparing to the two high end pieces of glass mentioned above.
With that being said, I don't regret purchasing them as they fit my budget at the time and I certainly feel I have received my money's worth from them. I did have one warranty repair when an eye cup came loose and Vortex repaired them in very short order with no charge to me other than shipping one way.
As my budget increases I am looking much more at the Swaro 10x42 EL's for my next set of binocs.
-Schism