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.
Jim M