My two cents worth and why I wouldn't have the cheaper one.
1. the cheaper one does not have automatic reset. Which means that if it trips out on low or high voltage you will have to manually reset it, (just like if a breaker trips out on overload).
This translates to: if you are gone for the day, and it trips out, nothing will be working in your trailer until you get home and reset it. Think how hot it will be in there on a summer day!
I made the mistake of getting the cheaper model with out knowing the above. My wife and I winter down in the Keys and go kayaking all day long. Bahia Honda State Park which is one of the places we stay at is notorious for spikes of low voltage, and it only took coming back to a hot trailer a few times for me to get rid of the el cheapo. I gave it away.
2. The expensive one has an automatic reset, but it also has an 8 second time delay to enable an AC unit compressor to work properly
Good luck on your decision
Jack L