The smaller brush makes it easier to get the smaller lashes.
Twice as much product as the Clinique brand with awesome staying power.
Loreal Telescopic is another great substitute. You may need some practice with the "spikey ball" applicator, but after a few tries, it is easy to control and even better costs under $10 at the drugstore for .27 oz. And you can most likely get it on sale or with a coupon. Bonus: you can also use it on top lashes and get into corners.
Overall, I like the idea of Clinique's bottom lash, but for the cost, I feel that you can find other substitutes that work just as well. Also, for me, I'm not generally wearing mascara on my bottom lashes at my day job, so I can't justify the cost, so I would rather use that extra money towards a high end foundation or eye shadow.