One Handed Keyboard makes it easier to type with one thumb, even on the larger iPhone 6 and iPhone 6 Plus screens by condensing the keyboard to the left or right.
Customization options: Through this app, you can quickly switch which side of the screen the keyboard is on at any time by tapping the arrow located next to the keys themselves. You can also change the color of the keys, which is a nice touch.
Size adjustment: The app condenses the keyboard down so that it takes up half of the width of the iPhone screen. There is no way to adjust the width of the keyboard further to make it just a little wider. On the iPhone 6, this isn't quite enough space to type comfortably. But this isn't so much of a problem on the larger iPhone 6 Plus.
Awkward operation: Because the keyboard is condensed so much, icons for switching back to a regular keyboard and for accessing the numbers and symbols panel are eliminated. There are just a few dots to the left of the spacebar to let you know you can tap over there. If you poke around enough, you'll find what you're looking for, but there's really no reason the keyboard and all of the buttons need to be condensed to such a degree. Spelling suggestions also only take up the same amount of space as the keyboard widthwise, making them hard to read.
One Handed Keyboard does what it promises in terms of making all keys reachable from one side of the screen. The execution definitely leaves some things to be desired, and it would be nice if you could customize the size of the keyboard itself to suit your particular reach and needs.