There are a lot of reasons why Nintendo's Circle Pad Pro, the hardware extension for the 3DS, might get on your nerves. It's an extra 20 bucks. It takes AA batteries. Most importantly, it almost doubles the size of the console!
Nyko's Power Grip Pro, the first third-party copycat of the peripheral doesn't fix most of those problems, but at least it looks a lot nicer than Nintendo's extra slab of plastic.
It does fix the battery problem, actually. Instead of requiring a few AA batteries just to operate, the Power Grip Pro uses a rechargeable battery pack to extend the 3DS' battery life. It also has a protective shell on the outside, so while the accessory makes the handheld bulkier, it also becomes more durable.
The Nyko edition is a little pricier than the Circle Pad Pro, $30 to Nintendo's $20. If you haven't gotten one yet, though. This will definitely be something to consider when it ships this October.