I do not think it matters in terms of overall plant growth, the energy required is minimal for this change relative the the total Fe requirement of the whole plant.
0.05% of the plant vs say 40-50% of the plant for Carbon from CO2.........which would you predict is far more critical to energy demands for acquisition???
The Seachem and Fe Gluc are the same products..........
As I understand it (always dangerous ), ferrous iron, Fe2+ is the directly usable form, for plants. The problem is Fe2+ is also less stable, needs to be dosed more frequently and is more likely to be adversely affected by water conditions, alkalinity in particular.
I know there have been some good discussions around here on the subject.