Which type of electrical protector is better for the appliances? surge or over/under voltage protection?
Multi-outlet surge suppressors are cheap junk.  Go ahead and watch a BigClive teardown on any of them, they are nothing but wires with a handful of small MOVs tossed on so as not to be blatantly lying when claiming surge suppression. Not surprisingly, the "famous brands" are rented brand names stamped on cheap Cheese junk.  

On the other hand, whole-house surge suppressors are made by names that are actually famous in electrical distribution equipment such as Eaton, General Electric, Siemens and Square D. Those items are Good Stuff.  

Tell you a secret. Nothing requires you to put them on your "whole house". Suppose you have an outside air conditioner. Those can be sensitive, but far more alarming, they can make spikes like crazy, so you'd want to protect the rest of the house from the air conditioner.  I would cheerfully install a "whole house" unit right at the air conditioner. That does not preclude putting another one elsewhere. 

My concern with a circuit interruptor for undervoltage and overvoltage is that it won't act quickly enough.  The spike will get through, and then you'll get a "nuisance trip" as it "saves" your PC by deleting all your work and killing your hardcore Diablo character.