This is a massively popular eyeliner that I feel has improved over time. Even though it's not the cheapest, the formula is definitely better than your average pencil/liquid eyeliner and it stays put. At the time of this review I am in Melbourne, Australia where the temperature is currently 42 degrees Celsius (107 Fahrenheit) and my eyeliner has not smudged, faded, or transferred on my lids nine hours ago. That is really impressive for someone who has Asian oily eyelids and can only wear waterproof mascara lest it smudges throughout the day. I find Western formulas don't cut the mustard compared to Japanese eye makeup products but this one happily does, and it's widely available in most drugstores.
That said I always use a high-quality eye primer (Inglot Eye Shadow Keeper or NARS Pro Prime) before applying any other eye makeup, which is essential. It goes without saying that the black gel liner will smudge a bit more than the brown one but both are pretty long wearing and will need an oil-based remover to take off at the end of the day.
In terms of how easy it is to work with this gel eyeliner I think it comes down to what kind of brush you're using and making sure the amount of product on the brush is appropriate for application. I always dip my brush into the pot, go straight to my hand, and take off any excess product so that the liner won't look too thick or uneven first time around on my lash line. I don't always use an angled brush either because I like to smudge it out for soft definition around the eyes; a tiny pencil brush is better for this kind of application.
If you're not comfortable having to use a brush for this type of eyeliner I wouldn't recommend this, but I find it a bit more forgiving than liquid eyeliner as you can smudge and alter the shape of the liner while it's still creamy on the lid. Once it dries, it'll stay there until you're ready to take it off. I like the brown color for normal, everyday wear and the black color for more glam/vintage looks and occasions.
Pro tip: If the product has dried out, mix in a few drops of Inglot Duraline to turn it back new. Take care so that the lid is screwed on tight and stored upside down when not in use.