I've been using one like that for over 3 years now. My camper is plugged in 24x7x365 as we are able to park it at home. I put it inside the cabinet where the trailer cord shoves into, shorted the cord and put on a new female end. I then plugged the protector in there and shove the protector female end out the hole. I then use another 30 amp extension cord outside the camper to plug into.
I have this set-up for over 3 years now. Plug in and forget. Either it's working real well, or it's not working at all, because we've never had problems with anything funky happening with our power. For us, it's worked very well. And like I said, plugged in almost 100% of the time for over 3 years now.
I recommend it, if you want protection without breaking the bank. Granted, it's not got all the bells and whistles like some of the more advanced ones, but for us, this works just fine.