Oh my, how I love this one! I am going to compare it to my MAC Prep & Prime Lash and Esteé Lauder Little Black Primer.

MAC PREP & PRIME LASH
Excellent for creating volume
Only works well with wet formulas due to being white in colour and needing to be covered up

ESTEÉ LAUDER LITTLE BLACK PRIMER
Looks nice and natural on it's own and does amp up length when paired with another mascara over top
Does not provide volume, dries super quickly (you have to work fast with this one) and kind of hard to remove

BENEFIT THEY'RE REAL LASH PRIMER
Wears beautifully on it's own
Does not dry stiff and allowes your lashes to be flexible
Gives a mega long and fanned out lash effect when paired with the They're Real mascara over top (my lashes have never looked longer)
Allowes you to finally remove the They're Real mascara without using a remover (unbelievable! I know)

I absolutely 100% recommend it!