I have been using fLash serum for about a year now and I love it. I have tried others previously but didn't get the results that I get with fLash.
Within about 3 weeks of when I first started using it I noticed the eyelashes looking longer. But as with all hair, the long ones would fall out and the new ones would come through.....so even though they are long for a period, it does then go through a phase of being a bit shorter again, but never fear, they too will grow.
I have noticed that my lashes benefit most having a break, so after every 2 tubes I go through, I give it a rest for a couple of weeks before starting a new one. Unfortunately I find the tubes don't last that long so you do need to keep restocking. Pity they don't make it in a bigger tube with more product in it.