Effectiveness of different supplement brands?

A friend of mine told me she got very good re­sults from Vi­tamin World mela­tonin, and lit­tle or no effect from Na­trol mela­tonin, and that re­minded me of re­cent news that many herbal sup­ple­ments don’t have any herbal con­tent.

Does any­one have in­for­ma­tion, whether based in per­sonal ex­pe­rience or from stud­ies, about which brands are more re­li­able about their con­tents?