Mind Knights are a more situational unit, and shouldn’t be spammed, but their role is important to protect Edia, slow down the board and force the opponent into awkward positions.
Their Shove ability is great to put enemy units in the line of fire of Edia. Invoke Fear is conversely good to deter the opponent from attacking Edia.
It’s expensive and poorly stat’d, but if you can make use of its board controlling abilities it is then well worth the price.