This Uni Pin came from one of my recent Jet Pens orders, as I indicated in this posting. My first impressions were that it looked good, the price, $1.65, works well with my economy pens budget, and I have read mostly positive reviews about it, too.
The ink, tip, barrel, and the feel of the writing itself all felt great. No complaints there. What surprised me is how much the ink spreads and bleeds, even on this 80g Rhodia paper (from the Rhodia Reverse Book). I have used pretty wet, medium point, fountain pens without this sort of result, and I think this could be quite messy on more porous paper, especially if you want to use the back side of the page.That being said, everything else was quite desirable, and I can see why this is a favorite for those who like to sketch or do technical drawings. Either way, I think comparable offerings, such as the Copic Multiliner or the Sakura Pigma Micron might be preferred in that they are less likely to bleed or cause show-through on the opposite side of the page.
My other major complaint is that the indicated tip size does not even remotely reflect what will hit the page. This ink spreads, and you are more likely to experience a line in the .5 (maybe even .6) range over the .24mm suggested on the barrel. I am aware that manufacturers indicate the tip size and not the size of the line, but usually there is a closer relationship between the tip size and line than I experienced with the Uni Pin.
The backside of the page: I rarely see any pen cause this on Rhodia paper, so I was quite surprised. If you don't use the back page - and I usually don't - this might not be an issue.
Bottom line: the Uni Pin is a great pen, so long as you understand what it will do for you. It will give you smooth, jet black lines. It will spread if you leave the tip on the page, and it will probably show on the other side of the page. I personally don't have much use for this pen, which is why it will also go in the next giveaway.