I've got a heavily planted tank with no co2   I did try it some time ago - I got the cheapy set like slt.  I only used it when the tank lights were on but noticed that during the night my fishies were hanging around the top of the tank too much, so I stopped using it.  Fishies seemed happier, they don't swim to the top of the tank at night any more, and plants are growing like crazy.  I know everyone says it's great for plants, but I manage well without, but that's just my opinion.