The higher $ item has more bells and whistles - more protection.
Progressive EMS-PT30C is similar to the Surge Guard 99 34750.
I installed a Progressive EMS-HW50C Surge Protector with Voltage Protection and Remote Display Hardwired for 50amp RV's. I installed a hard wired unit because I did not want to have a portable unit hanging off the power pole at the campground or off my RV box I have mounted on the outside of our garage.
I can turn it off (will need to when I connect my generator), indicates line voltage and current on both phases. Also frequency of power to unit. I removed the wall in the storage compartment area (cut in half and added a vertical support in the middle. My breaker box is "behind" the unit so the wire was easy to pull through. The original power cable to the breaker panel had plenty of length for connecting to the EMS-HW50C. Working with 6 gauge wire was a pain - especially feeding it through the current sensors and then connection to the unit.
Purchased mine from tweetys.com.
The bottom link is a video of the remote indications.
http://s1193.photobucket.com/user/norskecruiser/media/007_zpscf77424d.mp4.html
2017 Keystone Avalanche 320RS
TV - 2011 Chevy Silverado 3500HD LTZ CCLB Duramax SRW 4X4