The rewards all look pretty cool. Good to have a bridge between the strength of Eagle Eye/Mystic Might and Rigour/Augury.
The staff is also a great concept for earlier/med level players as it helps them with learning about Elemental Weaknesses as well.
And just to be clear, do the uniques come from both Bosses and the change in rewards are just with the common loot? Or is the Deadeye from 1 boss and Mystic Vigour from the other?
Each boss has their own uniques, a fire piece and an ice piece of the Twinflame Staff, one will offer Deadeye and the other Mystic Vigour - if you look at the imagery you'll see that Deadeye has a kind of 'frozen' edge and Mystic Vigour is a little singed at the bottom.
The common loot will vary slightly but they should mostly be flavourful differences and not material differences in profit.