Functionally, Guardian Sphinx works identically to how a Flip Summoned Flip monster would. It just doesn't activate from any other means of being flipped face-up. It's more apparent on monsters like Ghostrick Skeleton, which work IDENTICALLY to Flip monsters. They just aren't affected by cards like this, since they're not a Flip monster.
This card is active, no flip effects, man eater bug and hiro shadow scout become nothing but trash