The BLEFriend makes it easy to get any USB enabled device talking to your BLE enabled phone or tablet using a standard USB CDC connection.
In it's simplest form, it works on the same principle as a common USB/Serial adapter (the FTDI Friend, for example!). Any data that you enter via your favorite terminal emulator on your development machine will be transferred over the air to the connected phone or tablet, and vice versa.
Good question! You can get a Bluetooth 4.0 USB dongle from the store already, and it's a useful tool to have (particularly on the Raspberry Pi or BBB), but that won't solve some problems out of the box.
To start with, Bluez (Linux) has a decent learning curve (and doesn't run on OS X if you're a Mac user). Windows 7 doesn't even support Bluetooth Low Energy, and on OS X you'll have to sort through the native Bluetooth APIs and development tools that require an annual paid license and specific license terms to access. There isn't a standard, open source, cross-platform way to talk BLE today.
With the BLEFriend, you can be up and running in under and hour on just about anything with a USB port, with easy migration across platforms and operating systems. It's not perfect (it's currently a peripheral mode only solution), but it's the easiest way you'll find to get any USB device talking to your iOS or Android device.
The board is capable of much more than simulating a basic UART bridge (and this is still early days for the Bluefruit LE board family)! Thanks to an easy to learn AT command set, you can also create you own basic GATT Services and Characteristics, simulate Beacons, and change the way that the device advertises itself for other Bluetooth Low Energy devices to see.
To make sure that your device stays up to date and can benefit from the latest Bluefruit LE firmware from Adafruit, you can also update the firmware on your BLEFriend over the air using any supported iOS or Android device.
You can even pick up a sniffer edition of the board that comes pre-flashed with special firmware that turns your BLEFriend into a low cost Bluetooth Low Energy sniffer, capturing data and pushing it out to Wireshark. We currently offer this as a seperate product, though, since the firmware isn't compatible with the over the air bootloader used on the standard products, but we'll address this in the future with a tutorial for J-Link owners, allowing you to switch between modes using your SWD debugger.
There are plenty of BLE modules out there, with varying quality on the HW design as well as the firmware. We always try to keep the bar as high as possible at Adafruit, and one of the biggest advantages of the BLEFriend and the entire Bluefruit LE family is that we wrote all of the firmware running on the devices ourelves from scratch.
We control every line of code that runs on our modules ... and so we aren't at the mercy of any third party vendors who may or may not be interested in keeping their code up to date or catering to our customer's needs.
Because we control everything about the product, we add features that are important to our customers, benefit from being able to use the latest Bluetooth specifications, can solve any issues that do come up without having to persuade a half-hearted firmware engineer on the other side of the planet, and we can even change Bluetooth SoCs entirely if the need ever arises!
If you just want to get up and running quickly, this is the right guide for you, and the QuickStart section should have you up and running in no time.
If you're new to Bluetooth Low Energy, and want to get a high level overview of how data is organized and how devices communicate with each other, you might want to have a look at our Introduction to Bluetooth Low Energy learning guide, or buy Getting Started with Bluetooth Low Energy from the store.*
* Full disclosure: co-written by me :)