They do work and some work well, downside is they take out almost everything that is green. As said above, its a needless chemical.
Algae growth is an indication that you've got an unwantedly high level of dissolved nutrients in the tank. A mild increase in water changes, reduction in side-wall facing light and possibly some pre-filtering of water are called for. The easiest to control of these is the light.
I actually choose a side on which to grow algae in some of my tanks, this lets me use the algae to consume the nutrients then I can scrape it off and net it out with a fine mesh net.