Possible Duplicate:
When leaving Privet Drive, why did there need to be seven Potters?

Even after using polyjuice potion, there was a chance that original Harry got killed by Death Eaters (Later, we found that their trick failed too. DEs discovered who original Harry was). Why wasn't use of invisibility cloak favored?

Its true that invisibility cloak wasn't immune to Homenum Revelio spell. But, it was almost impossible for DEs to use this spell nonstop everywhere. What's the thumbs down point of invisibility cloak due to which Order ignored it and used polyjuice potion trick?