I love the ADA Aqua Soil Amazonia. If you have the money it's definitely the way to go IMO. The plants love it.
I have used flourite before. It is supposed to supply the iron. Otherwise it's inert. You will have to supply all the other nutrients your plants will need. In the tanks were I have a mix of flourite and ADA Aqua Soil I still add iron. Before I found the ADA A.S. I had used flourite and gravel for decades. It's ok if you need to conserve your funds, but you will spend in nutrients. The extra you spend on the ADA A.S. you can EASILY make back in plant sales.
Good luck with your tank!