These are similar to the red laser pointers, but much brighter. While the red lasers have a wavelength of about 660 nanometers (nm), the greens have a shorter wavelength at 532 nm. Because the human eye is much more sensitive to green light, it appears to be much brighter. This one was made in China and is said to have a maximum output power of 300mW. I doubt that it is really that powerful. But it is powerful enough to be awesome.
In the dark, not just the dot, but even the beam is clearly visible from more than 100 meters away; and the initial burst is much brighter. When used on a slide projected onto the screen in a normal class room setting, the brightness of the dot overpowers the projected words.
Something similar to this one is available on the Internet for about 60 US dollars. On Temple Street in Hong Kong, you can buy one for about 80 Hong Kong dollars.