I always used to wonder about water lettuce and if it would benefit my tank when I had one.
It wasn't until a friend of mine tried it and found just how quickly it would grow and how much you had to do to ensure it didn't take over the tank and cause oxygen depletion that I decided it probably wasn't the best kind of plant to have in an aquarium.
Water lettuce is fine if you have the time to be able to manage it as it grows pretty quickly and can take over fast.