Yes, it only protects the user from roadblocks set from other players, even if you land directly on it, though landing directly on Bob-omb and Thwomp roadblocks won't really affect you anyway, but the animation will still play. The Metal Mushroom Orb won't protect you from any of the yellow orbs (Orbs You Throw) that other players set. As Vip said the effect wears off when you land on the space before the trap activates. The metal mushroom will completely protect you from any of the roadblock orbs, which are the red ones. They can be distinguished from the yellow trap ones when placed as the character's/team's icon will hover above the space instead of replacing it. Teammates can't erase their own team's roadblocks in team matches with metal mushrooms just like they can't activate them incase you're wondering.
Here's a tip, if you're about to pass a Koopa Troopa (Paratroopas are called Koopa Troopas in 6 for some reason.) roadblock, it may be best to activate it instead of using a Metal Mushroom depending on the location of the player that set the trap. That orb can easily backfire.
