What lash serum works FOR REAL

Hi! After months of wearing lash clusters, they lost their strength and looks not so « strong », I did loose some but not a noticeable to others amount. Im looking to grow them longer since I stop wearing clusters and slightly feels insecure about my shortness and how not voluminous they look. So, what’s the best lash serum that is worth to buy? I bought one, I finished it, was consistant and all but nothing.

Thanks !!