The ‘Big Al’ model is about 2¼” x 3″, about the size of a small tape measure, comes with six ½” vinyl erasers and runs on two AAA batteries. The recommended retail is about $5 US.
It’s gentle – the vibration has the lightest touch and will remove pencil marks without harming the thinnest of papers, such as onion skin.
Things I don’t like about it:
It’s small – I loose a lot of things on my desk, at least with cheap erasers I usually find one eventually.
It’s gentle – you don’t have the option of applying elbow grease, if you press down, it stops spinning until you ease up. So if you are working on deep pencil you will have to resort to an non-battery powered eraser.
aside from that there is no reason not to add one of these to your tool box.