I too was skeptical at first. Then I purchased a Progressive portable surge suppressor. I have found that it has alerted me and also tripped saving my coach from high voltage situations, conditions where the voltage was low and the frequency of the electric coming into the coach was out of spec. And this occurred at well known campgrounds (Disney's Fort Wilderness, Hershey High Meadow campground, Boyd's in Key West and others as well). I would definitely recommend getting one.
Berniross said "I'm sure you will get lots of folks who say you have to have them. I've been RVing for 16 years without and never had a problem."
Maybe he just got away without knowing he had a problem. There was a situation at one campground where my air conditioners were not functioning properly. Went out and checked my Progressive unit and found that the electric coming in was at 101 volts- way too low to provide enough power to my coach. I had to move to a different site (this was on a July 4th weekend) for them find one that had the appropriate power. A number of others in the same area were unaware of any problems.
I for one will always have one.
JMHO.
2014 40' Forest River Berkshire DP Bunkhouse