The iPad accessory Keyboard Dock is a full-size keyboard with a dock (docking station) in-one.
With this combined unit you can synchronize (sync) your iPad and charge its battery. This is done by connecting this unit via a USB cable with your computer.
An alternative to charge the battery of this device is to connect the keyboard dock unit, through a 30-pin connector at the rear, to an electrical outlet or wall socket, through the iPad 10W USB power adapter.
If you plan to purchase an accessory somewhere, keep in mind that you look for the statement: Made for iPad.
It tells you that the accessory has been designed to connect specifically to this device and has been proofed by the developer to meet Apple performance standards.
The keyboard, featuring a firm metallic enclosure (aluminum) does not need batteries and works without being connected to any power. It allows you to work on your iPad in portrait view, e.g. doing document typing, replying to emails etc.
While doing this, having a stable surface is important especially if you are charging the battery at the same time.
So you will need a desk, table or counter when using this unit. Some will use a hard covered book when sitting on the couch.
Now here comes the wireless bluetooth keyboard in.
A lot of people prefer working with the wireless keyboard in stead of the keyboard dock unit because there is more flexibility. you can view the screen of your device either in portrait or landscape. besides that, the bluetooth keyboard is separate from the device so you can move the keyboard around without moving your device as well.
However, a wireless keyboard does not have the specific iPad keyboard interface options. you are free in you choice which wireless keyboard you want to use. Any Apple bluetooth keyboard will do.
So, if you are on the go or travel then the device plus dock and wireless keyboard (instead of keyboard dock) might be more convenient. It allows you to move around and also share bluetooth keyboard with other devices such as. iPhone 4.
Another keyboard-dock concern might be that future iPad versions will use a different dock, which happened with other devices of this manufacturer.