I'm a fiber specialist I bought a similar device under a different brand. Both appear to be from the same manufacturer. These units are very inexpensive but seem to last longer than a $200 VFL from a reputable manufacturer. I have 1mW and this one has 10mW VFL. 10mW is noticeably brighter when looking for light through the outer cladding of the fiber, but too bright to see defects in the cladding that protects the fiber directly. I rotate the case slightly to turn off the battery so the side switch doesn't drain the battery if it accidentally moves to the on position.