The Sekonic L-208 is the least expensive professional light meter on the market, and has been a standard for years as a result. I have been using mine for over five years. I use numerous older cameras, some of which have no integrated light meters, and the accuracy of those that do is unknown, or they rely on batteries that can not be found, or which are too expensive for the value they would provide. It's easier and, in the long run, cheaper, to master a single external meter that works with all the cameras.
Operating the L-208 is simple -- dial in your ISO setting, set the lever to "incident" or "reflected" light, hold the meter where you want to measure the light (pointing at the camera for incident light, or at the target for reflected), and press the button.
Pro: it works, and the needle indicates a range of choices, the shutter speeds appropriate for a complete range of apertures. The battery lasts forever. It's small and light.
Con: it is too easy to accidentally spin the ISO dial, resulting in nonsense numbers. The "incident/reflected" lever is unmarked; I added my own labels, otherwise I could never remember which way was which. When I use it in public places, people sometimes think I am using a geiger counter to test for radioactivity.
Though the device is entirely plastic, I have had no problems with reliability. If I should ever replace my L-208, I will get another Sekonic.