This serum definitely pumps up the volume of my lashes when I wear it under mascara. I've used it with Dior Diorshow mascara, and the effect is insane. In fact, my lashes look so huge that I do not recommend this product for the office...it's just too much!
While I did see an obvious volume and lengthening effect, I didn't notice any additional curl, which is something the product promises to deliver. I also think the serum goes on too thickly, perhaps because of the style of the wand. That can result in clumps, which will make your mascara look clumpy as well.
I've also used this serum as a nighttime conditioner. It definitely made my lashes softer, but I haven't noticed my lashes getting any longer because of this product.
In conclusion, if you're looking for a primer, this is a good one, but Lancome's might even be better due to the difference in the applicator wands. I recommend using this only for a night on the town, not for a day at the office. Finally, don't expect this product to make your lashes grow noticeably longer, because that just isn't going to happen.