I believe the formula of this is quite close to the popular Tony Moly's Back Gel liner. Same as with that one - if you go over one area enough times with the product (layer it a bit more), this is pretty much budge proof and can last for 12 hours. I usually use fine liner brushes, but the ones included (bonus points: it comes with a spare brush) can be used for faster application if you're not going for a really thin line and is really convenient for application or touch-ups on the go. The only downside is that the brushes are quite flimsy in the durability sense - if you usually carry them in your bag, some part of the holder or the brush usually breaks (same with the Back liner), but this won't stop me from repurchasing since I like the formula.