Chlorogenic acid, the active ingredient in green coffee extract, looks mildly promising for the millions of people who feel desperate to lose weight. There is one published study in humans, involving only sixteen subjects. This is a very small study, absurdly small, really. It was presented at a conference and has not been published in a peer-reviewed scientific journal. Doubtlessly, other studies are underway.
Pharmaceutical companies fund most research on new medicines and drugs, and these companies are only interested in multi-billion dollar profits from drugs that can be patented. If this were a drug that could be patented by a pharmaceutical company, believe me, the industry would be very excited about it. Chlorogenic is a naturally-occurring substance that can't be patented, so high quality research will emerge slowly.
You can read about chlorogenic acid at scienceDaily.com. Just search for "green coffee." There's a Wikipedia article on chlorogenic acid. Based on mouse and test-tube studies, it seems mildly promising. However, most promising supplements turn out to be worthless in the long run. You might remember chromium picolinate. Many millions of dollars worth were sold, on the basis of a few test-tube studies. It's probably worthless.
The weight loss benefits of green coffee extract, if any, don't seem to have anything to do with caffeine, even though it's extracted from coffee beans, among other sources. Chlorogenic acid is apparently not a stimulant.
Manufacturers with a brand name to protect will normally be careful to make sure that their products contain chlorogenic acid, as advertised. On the other hand, the FDA doesn't regulate the "nutritional supplement" industry very carefully, so cross your fingers. Some independent laboratories test some supplements and report to the public on their websites, but I don't think they're up to speed on chlorogenic acid yet.
Concerns about silica and other "fillers" are silly. If you're worried, it just proves you never took chemistry, or flunked it. Silica is a tiny amount of sand or glass, very finely ground. It prevents powder from getting lumpy, it's biologically inert, and occurs in small quantities in every kind of food, dirt and dust. If you pull an organic carrot out of the ground and eat it without washing it carefully, you're eating a lot of silica. Some manufacturers will charge a much higher price for products that are free of silica and fillers. Don't be a sucker - save your money.
Vitamin and supplement manufacturers have known for a long time that consumers are willing to pay about $20 per month for their products. Most of the green coffee extracts turn out to cost about $20 per month if you take 1600 milligrams per day, the amount recommended by "experts" based on the one very small study on humans. You've got to do the arithmetic. Number of pills per bottle, dose per pill, cost per bottle. Most green coffee extract works out to around $20 per month, as this brand does, assuming the price doesn't change (about $20 as of this review). Don't pay more than that. If you can find it cheaper from a reputable manufacturer, that might be tempting. If you lose even a few pounds per month, $20 per month is well worth it.
I'd like to lose some weight. I'm mildly hopeful. If it works for me, it will be great. On the other hand, beware of anecdotal evidence. I could be a shill for the manufacturer, after all. We'll know in a couple of years how much this stuff really helps. If it's any good at all, it will turn into a mad craze. Keep an eye on scienceDaily.com. They summarize most of the interesting scientific research published every day.
Good luck.