For freshwater tanks I highly recommend them. No fertilization and less sick fish. But DO NOT BUY THE ONES AT THE PET STORE, unless you like wasting money. You see, even if you keep them clean, they eventually loose color, and look even more fake.
Instead, go to Hobby Lobby. They sell all kinds of decorative fake plants that are created to look real. Pick out a few of the all plastic ones that mimic what underwater plants look like. I try to find those that are 50% off when I go in.
They have wire in them so they can bend and stay bent. Cut to size and trim about 1/2 inch or so of the plastic off the end so the bare wire shows. Put a bullet style fishing weight over the wire and bend the end. I can get 4-5 plants off each one I buy.
Super cheap and more realistic than the ones made for fishtanks. And instead of tedious cleaning, I just throw them out and get new ones. Less than a quarter of what you pay for the others, and easy to make.