I'm just going to start of saying, I have natural long lashes, so I didn't really expect anything major to happen when I first purchased this.
I used this twice a day throughout 4 weeks. I didn't see any amazing changes in terms of how long my lashes got. However, the lashes closest to me tear duct became a lot stronger and there appeared a lot more in that area (you can actually see that when you look at the picture from the first week and compare it to the fourth week). Though, my long lashes didn't grow longer nor did there come a lot more of them, they seemed a lot stronger - I felt that a lot less would fall out, when I removed my makeup. A thing I also really liked about this product is how my mascara would apply on top of it. It felt as if there was a barrier between my lashes and the mascara and it actually felt really nice. Also my lashes looked longer when I applied mascara on top of it. Now, that might seem like a contradiction but what I mean is au natural my lashes didn't look longer, but the difference between the serum + mascara vs. mascara on it's own, was huge.
Overall, considering that my lashes already were in a good condition, it still managed to improve my lashes in terms of how strong they are. I could live without it, but I like the thought of taking care of your lashes and not tearing to much on them. I would definitely recommend this and to prove it, I bought one for my mum for her birthday and she loves it as well! I bought mine on Fragrance Direct.