Some people report good growth with AS dosing EI levels of CSM but 6 months in, once the adsorption capacity has been reached, tox starts. The time before tox varies, some report up to a year, which gives people the false sense that EI is safe and causes no issues. It really depends on what you consider an EI dose. Is it 0.2mg/L of Fe as proxy or is it 0.5mg/L? Either is beyond excessive as submerged aquatic plants can't use that much. Regardless, AS should allow you to not dose trace elements for quite some time.
That downturn after ceasing traces is not a genuine deficiency even if it appears like it must be. Also, the importance of iron is way overstated and misunderstood to the point of ludicrous dosing of iron. I currently do not recommend CSM or any other comprehensive trace fertilizer until the nutrient ratios are determined through trial and error experimentation and tested across a multitude of species. Almost everything most people believe are wrong and unsupported in the scientific literature (e.g. EI, CO2, light, fertilization, toxicity and deficiency, etc.), even if some literature appears to support these ideas. A scientist never considers the conclusions of one paper in a vacuum; it's always considered in context of the body of research which can help explain why certain things happen.