As former rank 7 best Zed on EUW (before elo reset), I and many other high elo Zed players I talked to, will never build Duskblade of Draktharr on Zed. 
is 10 times better and you have more control over the added burst damage.
Duskblade of Draktharr is only viable for Talon, becaue he can do his complete burst within 2 sec.
Okay.
Well you know and 
isnt the idea to blow most of your chain on an opponent (open with ult, e +q) and then auto attack a couple times while your ult is running, which would trigger the item?
this should add quite some burst if timed correctly.
plus, it has otherwise pretty decent stats. high ad value and flat armor pen.
Ya the item is garbo. It's actually kinda okay on AD Jarvan because he can't quite kill you with his early game burst so the item solves his problem but it isn't needed late game when he gives no fucks about anything with his 1k damage+ ult.
I wouldn't say it it garbage but it is overhyped. The item is actually rather situational and is kind of a late game item imo. Works better as a counter to Squishies Building health in the late game than as a straight damage multiplier.
Great on Pantheon.
You can build both. Then you get two AD items for more burst.
Duskblade, Ravenous, Bork
Get all for big addition to your ultimate.
