I just say buy, buy, buy if you want darker eyebrows.
I am 58 years old and was a bit hesitant about whether it would work. But it did, see before and after picture.
I have been using it for 2 months now, and in the last few weeks I haven't needed to paint my brows, can only recommend.
Easy to use, I just swipe the applicator over my eyebrows every evening before I go to bed.
I also bought the serum for the eyelashes and there I don't notice the same result, but I will continue with it until the bottle is empty, the eyebrow serum I will definitely continue with.