Do you need buttons to play games on your iPhone? Certainly not. And yet, iOS MFi-certified game controllers are here, giving you the promise of full game controller-like support for games and letting you theoretically use your phone or iPod Touch like a little Nintendo 3DS or PlayStation Vita.
The Logitech Powershell Controller + Battery is one of those accessories. As its name suggests, it's a case that adds physical gaming buttons, and also has a battery pack. It also costs $99.99. For most people, that's where the train skids off the tracks.
Whether you want an iOS game controller probably depends on two things: how many cool games there are that support it, and how much it costs. At the moment, that's the failing of all iOS game controllers: the accessories, like the Logitech PowerShell Controller + Battery, simply cost too much. And what they do just isn't interesting enough...yet.
There are some stunning killer games in the App Store, but they're too few and far between. Add a few more supported games, drop the price, and then things will get exciting. Logitech's first entry into the iOS game controller accessory landscape is built well, but it doesn't have as many buttons as the competition...and it just doesn't feel all that useful as a result.
There aren't many game controller accessories available yet: the Moga Ace Power, the SteelSeries Stratus, and the Logitech Powershell. Both the Moga and Logitech are specifically slip-on cases for the iPhone 5/5s and 2012 iPod Touch that use a Lightning connector and add a battery pack to boot for on-the-road recharging. Both cost $99.99. The SteelSeries Stratus costs the same, but is a separate, standalone Bluetooth controller -- not a case at all -- and works with iPads, too.
The Powershell and the Moga Ace Power are very similar in some key ways: both require Lightning connectivity, excluding devices older than the iPhone 5 and fifth-gen iPod Touch, and both are designed as snap-on controller cases for iPhones and iPod Touches specifically. Both double as rechargeable battery pack cases. And, neither supports any Bluetooth connectivity. The Logitech case doesn't work the iPhone 5C; the Moga one does.