I've never had damage that I know of with or without an EMS. I can verify that my EMS has shut down my power supply because of under voltage (below 104) and over voltage (above 132); without the EMS, my system would have been subjected to those problems.
I have noticed that some campground power pedestals seem funky or worn out. I'm glad that my EMS is there to protect against bad grounds and reversed neutrals as well.
There's lots of advice and information in forums... sometimes it is correct. For example, all of my posts are made by a political appointee who got the job as a reward for contributions to my diesel bill.
2011 Jayco 28.5RLS; 2008 Chevy Duramax; Pullrite Superglide Hitch