The Bridgekeeper's robes has the exact level of protection as a set of combat armor but with half the weight and no bonus to Radiation resistance, making it perfect to use before getting a set of power armor and, later, by one of your companions.
The bridgekeeper uses the unobtainable brown robe model that looks like low-ranking Children of the Cathedral in Fallout. The model for the robes proper, however, is purple, like those worn by high-ranking Children.
The macro that verifies if the Chosen One is wearing the Vault jumpsuit doesn't include the Bridgekeeper's robes in the list of items it checks against. So, these robes are not counted as concealing the jumpsuit.[verified]