I use this brush with gel eyeliners, and only gel eyeliners. I doubt that it can be used with liquid liners as it has no bristles and won't be able to hold product. It creates an incredibly fine line, and is very precise. Doing your eyeliner with this brush is very easy, I prefer to use the side of the brush rather than the very tip.
A big advantage of this brush is how easy it is to clean, you can wipe it down quite easily, and as there are no bristles to stubbornly hold product.
On the other hand it is disadvantageous that as the brush has no bristles, it doesn't hold very much product, and to get a very dark line it is likely that you will have to dip the brush in your eyeliner again. This isn't a huge issue for me however if you like thick dark lines, this may mean that your eyeliner takes a few dips to do.
I did an eyeliner look using this brush to show how versatile it is. On the edges of my eye are thick smudgy smokey lines and on the top of my lids I lined very thinly.
Overall I'm a huge fan of this brush, but the only downside is that it doesn't hold much product and it's a welcome addition to my weaponry of brushes!