The case addresses a common complaint about the latest iPhones, which is that they just don't have the battery life that power users need — particularly for the smaller-screened iPhone 6 and iPhone 6s. Using the case essentially gives those iPhone users a battery life more comparable to what you'd see from Apple's larger Plus phones. Its design is also very similar to other battery cases from makers such as Mophie — products that Apple currently sells in its own stores — with just a couple of small touches to appeal more directly to Apple fans.
For one, it uses the same Lightning charging cable as the iPhone itself, as opposed to the micro-USB cord of most other battery cases. It also has what Apple calls an "intelligent battery status," which lets users know how much juice their phone and case still have from the lock screen.
From an aesthetic point of view, potential buyers should know that the case also has a bump on its back where the extra battery is housed. Some may find it unsightly. At any rate, it's not exactly a clean design, and so it may be best for those who value function over form.
Early reviews give the case a fairly good rating, though many note that Apple's case is not the highest-capacity battery case on the market, nor is it necessarily the best value.
Over at the Verge, reviewer Lauren Goode pointed out that the similarly priced Mophie Juice Pack has a 2,750mAh, as compared with the 1,877mAh you get from the Smart Battery Case — meaning that it has more battery capacity, and therefore can last you a longer time. And she notes the Verge's top battery case pick, the Incipio Offgrid Express, offers even more power for just $50.
Others say that the case is good enough, however, to address the iPhone's main weakness among Apple superfans. CNET's Scott Stein said that the case is nice and slim overall, though he was also not a fan of the bump. He also echoed other reviewers who said some non-Apple headphones may need extenders to get through the headphone port on the case. Apart from its price, Stein said that he liked the Apple case — but that the price was a roadblock for him.