It is our understanding that this product has pluses and minuses. Although results vary in studies, some have shown that it can be effective over the long term with about two to four applications each year over several years, but it must be timed correctly (before weed seeds germinate; immediate light watering after application and then a dry period needed) and it can be more costly than other pre-emergent herbicides. It would also depend on the size of the area where it was being applied. For more information, you might be interested in the following articles from the Cooperative Extension Service.
It is our understanding that this product has pluses and minuses. Although results vary in studies, some have shown that it can be effective over the long term with about two to four applications each year over several years, but it must be timed correctly (before weed seeds germinate; immediate light watering after application and then a dry period needed) and it can be more costly than other pre-emergent herbicides. It would also depend on the size of the area where it was being applied. For more information, you might be interested in the following articles from the Cooperative Extension Service.
https://www.extension.iastate.edu/news/2005/mar/mar0522.htm
https://cales.arizona.edu/yavapai/anr/hort/byg/archive/cornglutenmeal.html
Hope this helps!