The slide viewer comes with a USB cable (for light), or can be powered by 4 AA batteries. The viewer is bright and the magnification is somewhat helpful.
I used it to preview slides before scanning them. Slides are loaded from the top, and released using a button on the side. In my experience (viewing ~1500 slides) the mechanism to let the slides be released only works completely about half the time. The other half the time I had to turn over the device, or fiddle with the mechanism/slide to get the slide out.