I would be willing to bet that the MOV is there more to protect the electronics in the breaker or as Gar said to lower the tripping from transients then it is to provide TVSS protection for that circuit, while installing TVSS at the panel can provide some limited protection from surges coning in from the power lines, because of the high frequency nature of transient surges they will provide very little to no protection to event that happen closer to the load, this is why providing surge protection at the load is so important, any manufacture claiming other wise if just selling snake oil, some surge events such as near field lightning strikes that induce voltages into house wiring as well as networks and phone and cable will not be protected by any TVSS on the power lines even if they are at the load end. which also goes for TVSS installed on phone and cable lines, this is because this type of induced surge will treat all the conductors of a cable pathway as one conductor and the loop that can include the cable network and phone lines will develop a voltage difference of potential across the electronics within the equipment, so protection between the line neutral and EGC is no longer effective as all three will be effectively as one pathway for this induced current, also since it will also act like the secondaries of a transformer this current is no longer seeking to return to Earth so even Earth grounding has no effect, do a search on LEMP or lightning electro magnetic pulse.