They keep their customers' account secure by using state of the art encryption and storing their keys locally in a secure vault on their device.
It allows you to use multiple accounts, switch between all of them fluidly, for greater privacy and convenience.
They do a backup of your wallet so you can get your funds back in case your device is lost or stolen.
It's a free client-side interface that helps you interact with the Ethereum blockchain. Containing an easy to use open source platform allows you to generate wallets, interact with smart contracts and much more.