I'm an avid eldar player, back in the days I would normally choose Dark Reapers over Banshees as my first aspect warrior of choice. However now I almost never bother researching the reaper aspect stone, because
a) They don't scale into tier 2 at all well (compared to Banshees and their awesome CoW - fastest unit in the game!)
b) Their initial cost is higher - 210 for 3 guys comapred to 200 for 4 banshees I believe
c) The reinforce cost is similar - 70 req for one guy?? Possibly the most expensive single troop in tier 1?
d) OK they do decent damage if they can get set up and all, but for the cost and poor scalability, is it worth it? I don't think so.
I don't think any changes have been made to Reapers in DC so this applies to that too.