I'm not a user of Milorganite. Now what they say about plants needing micronutrients is true however, the metals listed in the post above are not essential micronutrients for plant growth. So you're adding them, likely in small quantities, over time to your yard. Probably not a big deal if you're not eating the soil or grass. I'd personally never use Milorganite in a garden. Plants are scavengers of soil ions and if you begin to accumulate these heavy metals above naturally occurring levels in garden soil you will undoubtedly begin to increase the concentration in garden produce.
All that being said, pick your risk tolerance and make a decision you're comfortable with. I'm not comfortable with adding heavy metals especially to a garden. The same goes for the product Ironite...that's some nasty iron mine tailings some people use for deep green lawn color. That one is a no way in hell for me. Milorganite is more of an indifference.