I love this product! I wonder how I did without it for the past 35 24 years.
Basically, its a teensy tiny brush, and its a "small" product but priced down accordingly I would say, at £10. I bought it in brown/black which unlike some brown blacks really is more brown than black, so suitable for fair haired, red haired, etc people too.
It goes on beautifully - totally clump free, and the teensy brush seems to "get" more lashes. The colour hasn't transferred or bled in the slightest and I did it at about 8am this morning, perhaps 9am, and I used eye cream this morning and no under eye powder or anything (only foundation) so that put that to the test adequately.
In fact, I used it on my top lashes for comparitive purposes - it doesn't "build up" in the same way a normal mascara does, so I wouldn't recommend doing that all the time because it would be, well, weird, but to be fair it still gave good definition and zero clumps. That's the key to this product - zero clumps, there really are no clumps of any kind.
You could probably use the brush once the product has run out - it would serve various purposes including an eyebrow brush, a lash combing brush, or even an applicator for the bottom lashes if you didn't want to repurchase but just use your normal mascara on your bottom lashes but with an easier application.
Well worth it - I would definitely recommend it, and can see myself adding this to my collection of essentials (and I would imagine all the other brands will launch their own versions soon if not already)