They're not magic... It takes time and it also depends on the entire gammut of features in your tank: light, co2, other fertlizers, water params. IF you don't have enough light, have too much light, or too little co2, you can add all the root tabs in the world and they won't change anything.
Not knowing what plants you have means we have no idea what kind of reaction they might have.
As for root tabs only helping "heavy root feeders".... This is nonsense. All plants have roots and anything in the substrate will benefit from a nutrient rich substrate of any kind, be it RootCaps, ADA, or other nutrient rich soils like MTS.