I think they are needed. Mine has only saved me once,, but that is enough to pay for itself. I have this unit and is just plug in and go. A lot of folks have units that are hard wired in the trailer, some with a remote mounted display. Most of the surge guards protect you from surge and also low voltages also,, which can be destructive. And I have never heard of a park assuming responsibility for a surge or low voltage problem.
I think Progressive Industries is most popular and they have a lifetime warranty.
My Geico Collision/Comprehensive policy excludes electrical breakdowns, but doesn't appear to specifically exclude damage caused by power surges. I suspect the difficulty my be getting the repair shop to attest to the cause. I'd guess that if a surge damaged multiple devices in my RV, it might be more likely that I'd be covered.
I opted to purchase and install the hardwired 50 amp Progressive and wired it between the transfer switch and the coach so I'm protected from the RV Park and any generator blips that might occur. I do have the display mounted in the kitchen of our Augusta and like being able to check volts and amps on both legs of the power.