We've had a couple of the cheap testers over the years, and yes, obviously aren't going to give the accuracy of the professional ones, but they do help if you think that you may have a problem area. I used one when I thought that we had a damp area in our last 'van. It confirmed the damp, which I repairs myself. It then confirmed that he problem was no longer apparent after the repair, and the dealer said that it was fine when checked with his pro kit when we came to sell it. So yes they do work, but it just depends on what you want from it.