People who have never lost $1,000 worth of equipment to a power problem often say they are not necessary. Would you rather risk thousands of dollars worth of electronic equipment in your RV, or spend
$250 one time?
As far as the 30 amp vs 50 amp outlet, your friend has a point. The 50 amp outlet probably has less usage so is less worn.
I've put my money where my mouth is. The link is to the unit that I installed in my RV 6 years ago. I have had it save my power system, probably, 3 or 4 times in that 6 years. If I bought another RV, I would install this unit immediately.