Both the Mandarin (Synchiropus splendidus) and the Scooter Blenny (Synchiropus ocellatus) are reefsafe fish that belong to the Dragonet family, and both are evolved to eat copepod.
Copepod are a small crustacean that live among the rockwork and crevices in your tank. They often become quite prolific when doing a traditional cycle, and can be seen crawling everywhere…until your first fish is added!
Copepod survive by hiding in the rockwork and emerging at night, however a Dragonet is adept at hunting them out during the day until it depletes the population.
The advice is to allow the copepod population to really get a secure footing before a Dragonet is introduced to the tank, which normally occurs when the tank is mature. To see how I feed my Mandarin fish, see this article.
My conclusion is a new system in itself can be quite stressful while you are learning the ropes, balancing elements, controlling excess nutrients, trying out the correct flow patterns and generally getting to know your system.
The decision to add a Mandarin or Scooter Blenny should only be considered once you are comfortable with your system and less stressed out by the smallest of changes.