Yes, we are talking about two different forms of iron. Ferrous iron, which is soluble, and ferric iron, which is insoluble unless chelated.
My experience with Flourish Iron (ferrous gluconate) is that it quickly precipitates out of the water column, which indicates that the ferrous iron is changing states and becoming ferric iron.
However, this may not be a bad thing. HeyPK has a very interesting theory that plants which require a lot of iron come from waters that contain high levels of iron due to water seeping out of soils rich in ferrous iron. His hypothesis is that the plants get their iron from the precipitate as it lands on stems and leaves. I am hoping to do more experimentation with ferrous iron in the hopefully not too distant future with this idea in mind. I also want to do a more in depth comparison between ferrous gluconate and chelated forms of Fe using plants known to require higher levels of iron.
Currently, I add both forms of Fe; a little ferrous gluconate from Flourish, and the majority from a chelated form, FeDTPA. My plants do well under this formula, though I often feel that I can further improve the health of my plants and continue to tweak things (I'm also by nature a tinkerer and find it hard to leave things alone
Adding Flourish Iron to your dosing regimen would certainly not hurt anything, and you may find that it improves the health of your plants. If you do decide to dose Flourish Iron, I would be interested in hearing your observations.