I put the Sakura Micron pen there for a size comparison – the Zebra pen is the same size, while the other 2 are slightly longer.
The tips! The platinum one is white because you actually have to put the ink into the pen yourself. Just a warning – the ink cartridge has a ball stopping the ink from flowing out, and you have to push it down (like the marble you see in Ramune soda bottles). When you do that, the ink splatters around so I would suggest doing it over a sink or some newspaper.
Zebra: It's pretty nice to draw and write with, and I like that it isn't too thick. It does get a little “fuzzy,” but I think that might be due to the paper I was using (index card). On watercolor paper, it did pretty well. If you use water right after inking, it will smear, but once it's dry, it is waterproof. The ink is also a pretty solid black. Overall, I think this is one of my favorites.
Platinum: I have mixed feelings about this one. One of the turnoffs for me was having to put in the ink myself, because as I said before, I got everywhere. Also, even though I screwed the pen back together pretty tight, some of the ink still leaks out and gets on your hand. If you don't mind that kind of mess, you might like the pen more than me. After I put in the ink, I had to shake the pen for a while to get the ink to the tip as well. However, once the tip had loaded with the ink, I really liked how I could do both thin and thick lines (although I think that's only when it was first loading – now it's mostly thick lines lol) One thing I like more about this pen, though, is how the lines are cleaner than the Zebra pen. The ink doesn't take too long to dry either, so you can use it for watercolor paintings. I think the ink for this is the “blackest” out of the 3.
Sailor: Probably my least favorite, but still nice. There's 2 ends, but honestly, there's not much difference between the two, even if one is “larger” than the other. I actually get more control using the larger end. Don't think I'll be using the smaller end anytime soon. The ink also isn't as “black” as the other two pens. However, like the other two pens, this one is also waterproof once you let the ink dry a bit.
Overall, they're pretty nice pens! They only cost $1.50 each, so if you feel like trying out some brush pens, I would probably recommend the Zebra one, since it writes/draws pretty well and doesn't leave a mess on your hands. (Don't need to worry about ink leaks in your bag if you carry it around, unlike with the Platinum).