I love lash serums, and of all the ones I've tried, this one was the most underwhelming.
The formula itself I found non-irritating/stinging which was a plus. The applicator is a skinny brush which does gather just enough product for application and it's very easy to apply to the lash line. It dries quite quickly and there's no residue.
Using it each night for 8 weeks, I had slightly longer lashes, but not fuller lashes. They also tended to grow unevenly - which could be my lashes themselves but I had one mega-long lash and the others were a bit slow with catch up. Made for problems with mascara etc.
While this brand is definitely cheaper than other premium lash brands, for the $64 and the reviews I'd read I was expecting something amazing, and it didn't happen for me.
I continued using till finished but haven't repurchased.