David W. Martin of CultofMac reviewed the MiLi Power Pack 4, and noted:
The Mili works just fine as an alternative power supply for your iPhone 4 or 4S, but it doesn’t offer the same level of protection that other slider power cases do. If you are careful and not prone to dropping things then the Mili might be a good case for you, but if you drop things a lot or you want something with more protection then you might consider something else.
David is spot on the good and bad of Power Pack 4. It’s designed to give maximum battery life to iPhone 4/4S, and the little kickstand offers great convenience, but it doesn’t offer protection to the top of your iPhone 4/4S.
You can find the full review here: http://www.cultofmac.com/131864/mili-power-pack-4-slider-case-packs-power-to-go-for-iphone-4s-review/