Milani Eye Tech Extreme Liquid Eyeliner is the first felt tip pen eyeliner I've ever bought so be aware that my review will lack a point of reference. I have no idea whether such liners can be any better or worse, this review will be based on my direct experience with this particular one.
I really like the packaging, which is a sleek felt-tip pen with an ergonomic grip. The pen has a long pointed tip which is capable of drawing a very fine line which can later be widened with additional strokes. It is a bit flimsy and I find it sometimes hard to control but with a bit of practice I think I'll be able to draw perfect lines.
The line drawn is intensely black and there's kind of glossy finish to it. It lasts all day without smudging or fading.
This product claims to be waterproof, so I did a water test. Under running water it didn't bleed or smudge but when wiped with a finger it came off completely, which means being caught in the rain shouldn't ruin your make-up but I wouldn't risk swimming with it on.
All in all I really like this eyeliner, the only reason I won't probably repurchase is that I like experimenting with things and I hardly ever stick to one thing when there are other options to explore.
Disclaimer: I bought the product myself for my personal use and I am not affiliated with any company. I am not paid to do this review and everything I said here is my genuine opinion.