How effective a protection is provided by “surrounding yourself with concentric mirrored spheres?”

This depends on who is requesting them and how they are to be constructed and implemented and maintained. If it is done by the person and their own energy through their own visualization, it will have limited power. It may be effective for low-level psychic attacks by low-level beings who are simply nasty and hurling insults, but it will not be effective against more powerful forces intending severe harm and having a huge energetic capability to mount attacks—that takes a considerable level of divine support to have a chance at maintaining protection. The same idea can be requested as a way of adding powerful intention by the person requesting this because the image it conveys will be reassuring, and that adds to the level of belief in the undertaking as well as the power in constructing the visualization to enhance the level of intensity of the request, all of which gives the divine realm a springboard to do its utmost to fulfill what is asked. In actuality, this is symbolic only and not implemented in that precise way by the divine realm answering such a request. It is the intention that matters, and how it is executed will be done by the divine realm in the highest and best way, and will not have something that can be reduced to a physical analogue, as described by this imagery, but that does not matter; what matters is the desire and the intention given to a request for divine assistance—that is what will bring success.