I had never heard of these things, but my niece had one and the little ones at home were attracted to it, so I decided to get one to have around the house.
It's kind of like a temporary "drawing board." You can use the included stylus or your finger nail, or almost any object to draw on the screen (the "print" is a light green color). There's something about the product that makes you want to draw. I have it next to my computer and use it mostly for quick computations and sketches. I've written reminders on it, but I stopped doing that because when the kids would see it, they'd immediately erase it so they could draw.
When you press the button, the screen flashes for a half-second and the screen returns to black. There's a cover that can be placed on the front of the e-writer to prevent accidentally erasing the image, and it also clicks onto the back. The stylus attaches to the e-writer, but it's a bit awkward to snap on.
Apparently, there's a battery in the e-writer, but I don't see any screws that allow it to be changed. I've had the e-writer for four months and it's still going strong.