Not these directly, but I do remember a similar wonder product a few years ago that has died a death.
Did a bit of searching and found this:http://www.diynot.com/forums/viewtopic.php?t=127788
now the second one has an axe to grind of course, and maybe the first.
But on the website for Schrijver they reckon 80% of UK homes have damp problems. I'm afraid that statistic makes me not believe anything else they say on their site.
Edit: another possibly biased opinion:http://uk.answers.yahoo.com/question/in ... 655AApfSfn
and this one which appears to be quite official from Australia which says this kind of thing doesn't work:http://www.heritage.nsw.gov.au/docs/mai ... ngdamp.pdf