Yes, but if you think outside the box for a quick second here...
Knowing that the enemy knows what this ability does just allows you to manipulate that fact. Pair this ability with other abilities that swap places with images for instance. (Like the Refractionist hero in my map /flex.), you could pretend like you 'are' one of those images, meaning the opponent won't bother with you. Or, the free windwalk just allows you a 'Get out of a corpse walk free' card.
whats the objective of making this spell if the enemy would know that the hero that casted it gets invisible and that he isnt one of that illusions? U know that abilitie of the Phantom Lancer that creates an exactly illusion like him and makes him invisible? that is realy usefull cos the enemies dont know if it is realy the hero or just an illusion...