Really, I've read from many sources that EC doesn't really have a lot of nutrients. Maybe some micronutrients (Fe and such), but certainly not much of the major nutrients plants need to thrive (N & P), and limited K, enough such that I wouldn't trust it to be the primary source. Aquasoil, other nutrient laden substrates (I think Fluval has something out now), or MTS/Dirt would be more what I think of when people say nutrient containing substrate.
I would 100% advocate root tabs, especially if you have heavy root feeding species (crypts, swords, etc). You will need water column ferts though. I highly recommend dry ferts for high tech plants, as they allow you a degree of control over your tank that premixed fertilizers, like Flourish, simply cannot. You'll also save bank on the medium to long term, as with Flourish you're mostly paying for water.