Duskblade is too cheap (some math inside)

Its stats (without the passives) have a gold value of 2596.67 (from lolwiki)

Its passive gives an additional burst of 65-320 damage (depending on level). Assuming a full rotation, the bonus AD required to get that same bonus damage would be (assuming a full spell rotation and no vision resets):

• 10-51 AD on Talon (350-1785 gold)
• 16-79 AD on Zed (560-2765 gold)

Which brings its gold value to (1 AD = 35 gold, again from lolwiki):

• 2947-4382 gold on Talon
• 3157-5362 gold on Zed

Buying Duskblade costs 2900 gold, so unless the vision passive is a hinderance which lowers the worth of the item (and it absolutely isn't) we can say that the Duskblade is too cheap for the power it gives TO THOSE WHOM DON'T ABUSE IT by stealthing mid-fight (thus resetting its passive).

For comparison: Luden's Echo's stats have a gold value of 2570 (from lolwiki) Its passive gives an additional burst of 100+0,1*AP damage Assuming a full AP build (600 AP circa), that's 100-160 damage (depending on AP)

Assuming a full rotation, the bonus AP required to get that same bonus damage would be (assuming a full spell rotation):

• 44-71 AP on Lux
• 43-70 on Annie

44-71 AP have a gold value of 957-1544 circa (1 AP = 21.75 gold, again from lolwiki), which brings Luden's gold value to 3527-4114 circa on both champions.

TL;DR Buying Duskblade costs 2900 gold and is worth (without the vision passive) 2947-4382 gold on Talon and 3157-5362 gold on Zed For comparison, buying Luden's Echo costs 3200 gold and is worth (all included) 3527-4114 gold on Annie and Lux