Great for underneath colored mascaras or mascaras that need a little pick-me-up
Since I have naturally almost-black eyelashes, it's hard for the colored mascaras I have to really pop and show their true pigmentation. This primer coats your lashes in white product that can get a little clumpy, so make sure to wipe off the brush prior to application! This adds a good amount of volume and makes your lashes the perfect canvas for color.
Another great use for this product is to really add some "oomph" to any less than superior mascaras you may have lying around in your collection. Just make sure to let the primer fully dry before layering your mascara on top!
Does an alright job
I don't think this product is really a necessary step for me. What it does do, is add volume. It's great if you have a favorite mascara, but want a little more volume or want more of a false lash look. It doesn't add a lot, if any length to my lashes. So I only use it occasionally, when I want super massive lashes!
If you have short, thin lashes, this product may work wonders for you. Since I have naturally long, thick lashes, it doesn't make much of a difference.