Well, I have a Maxx-com unit. I picked it up for $20 at a junk sale. I expected it to be of litle use.I should say I'm a marine radio operator, just sat my amateur exam.
What I've found is this: I can throw a 15 meter wire over a tree, connect the Maxx-com, ground it through a house earthing wire!! throw 150 watts into it from an Icom 700Pro and happily talk on the marine bands (mainly 4417 and 6224) to boats all over the Pacific,up to more than 2000 miles away, with signal reports much the same as the coast station running much more power into a bunch of dedicated antennae.
Who cares what's in it,who cares what the efficiency is,who cares what I could do with a lightbulb on top of a telephone pole or a resistor loading a whip??? The point is this thing actually does whats required,it enables me to very simply set up a test antenna system that works,is incredibly robust, and on my next boat will be my ATU. I'd much sooner use this than an ATU that might break, might get full of seawater, costs me a lot more and may be the one thing that stops me transmiting in an emergency.
All the tecdhnical discussion of lack of efficiency etc are largely irrelevant, everyone seems to be missing the point that the purpose of radio is to communicate, and this allows communication, simply,robustly and on any band.
I suspect they're hugely overpriced at retail,and the Maxx-com site is full of BS, but they do do a job well enough, and are potentially so much more reliable than conventional ATU's that I can't figure out why so many people waste their time calling them rubbish! Hey guys, they work!!! If everyone knows so much about them, then why don't some of you build the same thing and bring it to market at a fraction of Maxx-com's price?? I'll find lots of buyers for you.
One last puzzling thought,Icom sells a MN-100L "magnetic balun" for matching longwires on HF that sounds very similar in concept to a Maxx-com, if it's snake oil, how come it's as expensive as their autotuners, which contain a mass more electronics?
I don't think Icom are in the snake oil business...or are they??