I quite like both of the Reward Units...
Shao = Is a Min-Cost Gold Archer, Once leveled up and with +100 Attack Affection Bonus her Base Stats should allow me to comfortably retire out either or even both of my CC'd Silvers. (I only ever fused each of them with one self copy for the guaranteed cost down /skill up) Handy as I could use them for Awakening material for a Platinum Archer. It is a shame that her skill is only 1/5 not going to be able to spare any rogues to try upping that for a long time. [To be Honest she's not a great Gold only only slightly better than a comparable Silver and when most of us have a few platinum archers already she's not going to be a key player in most peoples units. Although if your struggling to clear content then she may be a more valuable asset because if you stack heavy on the death effects and RNG smiles at you then you can clear stages and even gain higher star clears than you would normally.]
Shuka = Is a good unit even now as at Min-Cost (16) and 3/5 skill +8% = 45s... I had some Rainbows hanging about so used 4 to get her to 5/5 for +10% for 60s. Her class effect is cost reduction to unit placements once she's deployed. (-1 / -2 CC / -3 AW = I believe) I don't see me using her to much for her cost saving right now given her lowish stats making her a bit fragile. But she could be part of a possible swarm play when combined with other cheap units. (3 Cost Copper Units or Soldier/Rogues/Monks for 6-11 etc...)[Basically you would want to be dropping several units after her to gain the most CP advantage from her.] I think she will be a valuable unit when we see grand marches being able to boost the attack of your entire deployed force should allow you to endure the peak waves better.
[I was wondering if her CP reduction will affect withdrawal values. If not then that's another way you can gain CP advantage ]