An EMS or whatever you want to call it, as said many times, is a great idea and cheap insurance.
You can either get a quality US made Progressive Industries one with a lifetime warranty or one of the off-shore models with a 1 year warranty. Based on warranty alone - easy decision....
One thing I like about the PI EMS is that it shuts you down at 104 volts while the other popular one shuts down at 102 volts. 102V IMO is too low. I read in one AC manufacturer's manual recently that anything lower than 105V can cause damage and I've found that 105 is a commonly mentioned threshold where you should manually shut down if you don't have automatic protection.
Progressive Industries have a number of additional features as this chart shows:
Progressive Industries versus SurgeGuard This makes it even easier to decide. :)
To add to this, don't be thinking that you will have the ultimate electrical protection by using an EMS (or equivalent) though. One other thing to be aware of is a "hot skin" and "bootleg ground" condition where a pedestal or outlet at a house can be improperly connected or you have a faulty shore power cord. An EMS will not detect these. This website is where to find out all about it:
Hot skin info. and
Bootleg ground info.You can also search username "jmsokol" on this forum. A non-contact voltage tester is a good tool (inexpensive too) to have in your RV.