Heavily promoted packs in magazines etc. are not necessarily better, they may contain a low potency saw palmetto and therefore are cheap to manufacture, but they have very big advertising budgets. Similarly very low costed packs may not have enough saw palmetto in them to make any difference to your prostate. Clinical work has been done on beta-sitosterol, one of the constituents of saw palmetto. A Lancet report indicated that it had a positive effect on prostate tissue. That and long term herbalist use, plus the use of the equivalent homeopathic titrations, means you can be certain that saw palmetto is not a 'snake oil mans' product.
Adverse effects appear to be almost nil, with only occasional advice re constipation.
You will find that most of the packs available are combination products in that they contain other herbs or vitamins which the manufacturer feels could enhance the basic saw palmetto, a shot gun approach if you like. Extract from rye grass pollen. Willow herb, saw palmetto, Juniper berries. Saw palmetto extract. A combination product.