I have an autoformer. It does the same as the Franks unit. I used it in a campground a week or so ago on 30 amps as my 50 amp cord wasn't long enough. I have a volt meter plugged into a kitchen outlet and noticed quite a difference when I eventually put the autoformer on line. It kept the incoming hydro where it should be. I did break down and spent a bunch of sheckles on a 50 amp extension after the better half kept forgetting to shut the AC off while using the hair dryer, microwave and therefore blowing the breaker at the pole.I had to hire a string boy to carry the 50 amp extension
. My autoformer was bought a few years ago and only works with 30 amps. I do have surge protectors for 30 & 50 amps but did learn from this forum that I can plug in a 50 amp to 30 amp dog leg after the 50 amp surge protector and will be protected on 30 amps.( I hope I got that right)