The brush is pretty cool if I do say so myself. Being the little dork I am I think it's pretty cool that is kind of square shaped. The brush has 4 distinct flat sides which makes it really easy to grab onto every lash. The front is kind of tapered and smaller to be able to reach into your inner corner. I still have to turn the brush quite a bit to get the little ones in the inner corner. The synthetic bristles are able to pick up and coat every lash evenly. 

The formula is pretty good. I think its the right consistency where it won't weight down your lashes and it dries fairly quickly so you don't have to worry about it getting on your eyelids. The formula is buildable but if you add more than 3 full coats, it will look kinda clumpy in some areas! Occasionally I get some little globs on my lashes since I usually scrape off excess product before applying and don't clean the rim (shame on me).

I do find that it is waterproof. Even in rain, it will not budge or flake off. It will not come off until you properly remove it. Every now and then around the 9 hour mark, I might get a few stray black specs but no biggie in my book!

It is also easy to remove even though it is waterproof. I use the Up and Up brand makeup remover from Target and have no problems. It doesn't create a runny black raccoon-like mess on your face at all and comes up in little black clumps that are easily wiped away.