A very good addition in my opinion...
The basic choice is hardwired or plugged in. No right/wrong answer.
In all cases will protect your rig from under/over voltage. Verifies correct wiring of the pedestal before sending power to rig. Most (if not all) have a delay before providing power to coach - intended to protect refrig/AC if the power flashes briefly (off/on of refrigeration equip while compressor was on can damage.)
Hardwired requires a little more to install (must be comfortable working in electrical boxes). There also may not be a way to bypass on newer models if there is an issue with the device (older units had a bypass that at least some manufacturers have done away with.) It also may have an electrical hum when operating. Obviously more secure as it is wired into your coach.
Plugin connects between your rig and the pedestal. No wiring needed, easy to bypass if needed. They are designed to be outside. In my case at least want to be in vertical orientation.
I use the TRC SurgeGuard - and chose the plug in model primarily for wanting to have a bypass option, and not wanting a 'hum' under the bed (where my power connections are). I use a chain/padlock to secure it to pedestal (no place to pass chain through on the unit, but wound tight they would need to cut the plug off or cut the chain...)
Surge Guard 50A Portable with LCD Display | Technology Research, LLC
It has saved me already - found a power issue at a campground resulting in low power on the leg I was on... Cut off the rig rather than having low voltage cause problems... Campground found the issue of loose/bad connection in main breaker box once I let them know.
(and I'm sure other times I'm not even aware of...)
I use a whole house surge suppressor in my sticks/brick home - that I wired into service panel - and have watched 2 units give their life in a surge to protect the house in last 15 years (while many neighbors had electronics damaged). I was in the basement about 15 feet away when one did... Was quite loud as we got a surge with power coming back on after an outage - but nothing else in the house was damaged.
Top of my list for the new house.