Meh, Merger doesn't allow you to do much, but moving around and picking time for attack. You still can be damaged by enemy attacks. Since there's no friendly fire in game it's easy for them to check if you are real ally or not. Mimicry last only 6s if you constantly moving. It takes 3.5 more time to regenerate the same amount of charge you use. You shall stand still during it, therefore might get detected. Also, illuminate makes you an easy target, if you try to regen your meter.