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.
But the Logitech Powershell doesn't have the same number of buttons as the Moga Ace Power or the SteelSeries Stratus; it has only a directional pad, four color-coded and lettered buttons, and two top shoulder buttons (plus a dedicated Pause button and on/off button for the iPhone/iPod that's inside). The Moga and SteelSeries controllers have extra dual analog pads and dual analog triggers, matching the "Extended" controller profile baked into iOS 7; this Powershell adopts the more minimal "Standard" layout. Apple has allowed game controller makers to pick either button-set. Honestly, there should only be one: the “Extended” layout, with all the buttons a seriously gamer would want. If I want to add buttons, I'd prefer to have all of them.
Will the Powershell have enough buttons for you? Maybe not for those looking to play a complex first-person shooter, driving, or flying title, but this controller has some surprises up its sleeve. All the buttons are analog, not digital; they're all pressure-sensitive. In Lego Lord of the Rings, for instance, one of the games I tried with the Powershell, holding the D-pad lightly to the left made my character walk, while pushing harder down made him run. This could mean that the shoulder buttons or front-facing buttons would work to control a pressure-sensitive gas pedal in a driving game.But, I'd still prefer at least one analog stick. The shoulder buttons feel stiff, too, unlike the smoother, more triggerlike secondary shoulder buttons on the Moga, which feel like the ones on the back of an Xbox or PlayStation controller.
You can still use the iPhone touch screen and accelerometer while playing, and certain flight games and action titles like Sky Gamblers: StormRaiders end up mixing tilt, touch, and buttons much like PlayStation Vita and Nintendo 3DS games already do. So, the lack of some extra buttons isn't always a huge deal breaker. Complex games like Grand Theft Auto: San Andreas end up playing decently, too, but using a D-pad instead of a proper analog pad just doesn't feel the same.
All basic iPhone/iPod functions are still accessible while the Powershell is on: volume, on/off, and camera access via a cutout section on the back. Headphone access comes via an included plug-in that juts out of the jack.
The Powershell's case feels compact with a soft rubberlike finish, made with the type of polish you'd expect out of an iOS accessory. The buttons and triggers felt very solid, too. The Moga Ace Power, by comparison, felt a bit more plastic and loose-fitting. I like how it feels when I hold it, too. If the Powershell had analog pads, it would be perfect. But it doesn't.
But, as a battery pack accessory -- part of the Powershell's supposed appeal -- it just isn't practical. It's long, unwieldy, and while a flashing color-LED indicator on the back shows when the 1,500mAh battery is fully charged, there's no easy way to tell how much battery life is left when in use. Mine ran out of juice one day, randomly. The controller still works when connected and should offer close to a full phone charge, but I prefer something like a Mophie instead.
What controller cases like the Powershell truly need the most are more great games on the App Store that work with them. Right now, despite a promise of "hundreds" of compatible games, I have a hard time finding 15 great ones. If you're a desperate retro gamer and don't mind being an early adopter -- and don't like analog sticks -- the Powershell might be for you. That's a pretty narrow subset. It's not a dream gaming device right now. I'd wait.