I have had a progressive industries unit in all my trailers except the tent trailer. You can search for threads and I believe you will see both sides of the needed/not needed fence on here. Is it cheap..no, will it potentially save you a lot of money...yes
I believe the high/low voltage protection has been a real benefit to me as we have had unexpected issues in campgrounds where it was very unexpected. Not needing to fix/replace our fridge/micro/AC/Tv's stereo etc is hard to quantify The damage done may be cumulative or fry it the first time you get bad voltage or an improperly wired post. Truly this is insurance and the choice is yours whether insuring your electronics is worth it to you.
I am a happy customer
Daryll