For most applications calling for a MOV or TVS, the voltage is high or is AC so comparators are generally out of the question.
Although you can 'add' the voltage of MOVs in series together to make a higher voltage, the resulting clamp voltage is less defined because of the increased resistance when conducting and the rather unpredictable sharing of breakdown voltage. A single suitably rated device will work better than two or more in series but if there s no other option you can use them.
Brian.