So first about the ease of use. The liners don't have the finest tip, but the shape of the tip allows for very thin lines to pretty thick lines. Two sides of the tip are flatter and wider, and the other two sides are more narrow. The product is also pretty thin and liquid so you don't have to drag your eye lid.
Now the pigmentation of the liners vary. As you can see in the swatch picture, Sabochan (black) is nicely pigmented. Carina (plum purple) is very, very sheer. Rodine Love (white) is right in between the previous two. I'm pretty disappointed with Carina.
The consistency and stay of the liners is very liquidy. You can see in the pictures that all the liners started to move into the crevices of my hand. It also takes quite a while for the liners to dry so you probably won't want to open your eyes right after applying the liners. However, once the liners dry, they don't tend to smudge or move. Unless you vigorously rub your eyes with water.
The packaging is obviously really cute. The cap can get dirty though.
Overall, there are better liquid liners than this one. I'm not sure about other pen liners because I've only tried a couple and I quite like Sabochan, so I wasn't totally upset. I do recommend other liquid liners with felt tips like Lancome Artliner and the MAC Superslick Liners (reviews and swatches will come :D). If you really want to try the Tokidoki Perfetto Liquid Liners I can really only recommend, from the ones that I've tried, Sabochan, because it's pigmentation is far superior compared to the other ones.
I hope this was helpful, thanks for reading! Byebye. C: