ETDA and weaker chelators or ligands do NOT break down instantaneously.
So if you dose daily etc, or if you used say DTPA 2-3x a week, the results should be similar.
I use ETDA, Fe Gluconate and DTPA all in one.
I buy Fe Gluconate and DTPA and add to Plantex CMS+B.
Cheap and will last about 5-10 years for maybe 50$ worth.