Personally, I find $135 for a couple of feet of copper wire, some PVC pipe and a printed circuit board from first science and surplus a bit steep. I wonder if they sell snake oil too.
Not doubting dousing, but you either have it, or you don't. I think people are giving them good feedback because they are embarrassed about spending that much money for what they get.
Dowsing does work to find anomalies but not specific items.. A bent coat hanger will work as well as any so called electronic dodad .. I haven't tried witness chamber type but I believe the results would be the same..