i appreciate what you are trying to say, and yes your are spot on, the only true guage is to remove the engine and do a proper job.
the link you have supplied is kind of useless tho, as they are trying to sell the item so it will obviosly be the best on the planet. they wouldnt exactly sell many if they said it was of an average standard and would match many of the others available.
The false results dished out country wide are not so much the machinery but the operators themselves. there are ways of falsifying results, thus you get a nice big figure and are chuffed then tell your mates, they use the same people in the hope of again nice big results and the loop of dragging in extra trade starts. its the oldest trick in the book and over the years i have found myself travelling upto 3 hours just to get to a r/r with a no frills you gets what you gots attitude after being ripped off many times and learning the hard way myself without any advise from others
Dan