Voltage can drop so low that incandescent lamps dim to 50% intensity. Even that is ideal voltage to all electronics. Voltage variations (watching voltage go up and down) as describes are near zero. Voltage will always vary only by near zero amounts because too much variation is harmful to motorized appliances (ie refrigerator).
What happens when AC voltage drops to less than 50%? Electronics simply power off - without damage. What happens if AC voltage varies more than near zero? AC utility cuts off power so that larger variations do not damage what is at greater risk (ie refrigerator, air conditioner, washing machine).
How does that Autovolt stop what three miles of sky could not? It doesn't. It does not even claim protection from sruges that typically do damage. Again, it protects from surges already made irrelevant by existing protection inside electronics and refrigerators. Autovolt was recommended by a salesman who forgot to mention what is always necessary - specification numbers. Why did a salesmen forget to mention normal voltage for electronics is even when lights dim to 50% intensity? Did he fear losing an obscenely profitable sale?
Where are spec numbers that says an autovolt will stop 2000+ volts - a destructive surge? None exist. Where does it claim to absorb (make harmless) surges that are hundreds of thousands of joules? It doesn't. But somehow it is recommended to do what even the manufacturer does not claim it will do.
Voltage variations do not damage electronics but can threaten motorized appliances. Surges require something completely different that, to create confusion, is also called a surge protector.
You obviously do not live in the DR. There are many parts of the DR where the wiring is insufficient in guage or the step down transformers to AC line voltage are not large enough and the voltage can be continuously low and it does destroy motors and compressors. I had wiring run to a different transformer exactly for that reason which I paid to have done. Edenorte would have done NOTHING about the problem.
Other people use whole house voltage regulators to bring the voltage back to normal. Thankfully my area does not have problems with over-voltage spikes.