I've only used one bottle, twice daily. I didn't purchase it for dark spots, but I thought it was good for my skin overall. This seems to be true so far. I love the scent, though initially, I thought it was too strong.
I do not care for the delivery of the product, though I cannot recommend another solution. Because of the consistency, I do not believe tubes would work. I do not like the fact it is extremely difficult to get the remainder of any product from a tube, so essentially I'm paying for something that I throw away because of lack of access. Their container extraction top does not reach to the bottom of the bottle, so the same problem exists. I take the lid off and turn the bottle upside down to remove the remainder. If they make the tip of the eye dropper reach the bottom of the bottle, this would resolve it. I hope my comments help.
Bottom Line: Yes, I would recommend this to a friend