I have the ~$200 TRC unit, got a pre-owned deal from a local couple who had upgraded to an RV requiring 50-amp service.
It definitely creates peace of mind for me. We had it trip multiple times for low voltage while staying at the North Rim (Kaibab CampeRVillage). This was in moderate temps and virtually nobody was running air conditioning. So I knew I could NOT run mine safely (and the managers were in the "I don't care" mode during our visit).
It also helped a week ago when we were at a non-traditional spot and plugging into a regular outlet (via an adapter). We could enjoy the TV and microwave and not worry that we could damage the trailer.
I take it a step further and test any outlet before I get started. My process is typically in this sequence:
1) Turn off breaker(s). Then turn them on/off after each step as appropriate.
2) Plug in a 3-light tester to verify the polarity is correct and ground is present.
3) Switch out the 3-light tester for a plug-in voltage indicator
4) Hook up surge protector, cable up RV, then final turn on of the breaker
DW is usually inside setting up things and knows the "click" of the surge protector being happy. She'll then set the clock on the microwave and that becomes our telltale for if the protector has had any issues.