I have a very love-hate relationship with these eyeliners. First of all we have the packaging. I actually like the outward packaging, but as you can see from the image below and to the right, the idea behind this packaging is that you can just draw on the perfect cat eye, while using a gel liner (as opposed to a liquid felt tip pen). But I feel like it doesn't work the way it supposed to. I just have a really hard time getting a clean nice line from this pen. Which is where the effectiveness aspect comes in. The sell with this liner is the packaging, which I don't think it very effective.
However I do love this stuff. There is a reason I own 4 colors! The liner is a super smooth creamy gel. I just use a thin angled eyeliner brush to apply it instead of the pen. Housing it inside the pen keeps it nice and creamy (however if you don't put the lid back on tight it will dry out, just like others). It stays put all day, it doesn't get on the top of my eyelid and it looks phenomenal after my other makeup has faded. They used to only have black, but now they have brown, purple, blue and green as well. I love them all! Even the green (which I was skeptical about at first) is really beautiful and wearable. But that is how all the colors are. Most colored eyeliners are either and almost black version (a super dark plum or blue/black) or they are super bright and loud. These liners are the perfect shades. The purple for example (my personal favorite shade) is definitely purple, but it isn't super in your face, it is wearable and BEAUTIFUL! I am a definite fan! Overall I do recommend these, especially if you are looking for one of the colors.