My new camper came with a Jensen that was about as useful as a plastic bowl. I mounted a fixed mount Jack antenna to replace it and was floored with the difference. I had a winegard sensar on my previous trailer and the fixed mount Jack pulled in more channels than even the old winegard. Immediately I ordered the replacement head for my dads class B that has a non-winegard batwing antenna. He also saw the same results. You definitely want to get the signal meter to put in-line so you can see where you get the best signals.
I recently put a Jack antenna on the roof of my house and am seriously disappointed with it. I can get 20+ channels on my camper with it sitting in the driveway using the Jack. With the Jack on my roof I can get 2-3 channels in my house. I haven't called King Controls yet to start diagnosing the issues but I will.
Buy the Jack, don't even hesitate. PPL motorhomes has the best price and they ship fast.
Fred