Zento Pen Series Review: Uni’s Low-Friction Gel Line

Uni’s new Zento series has been generating a surprising amount of buzz in the stationery community, thanks to its low-friction ink system and three-model lineup aimed at different writing styles. In this review, we break down what sets the Zento apart, how each model performs, and how it compares to Uni’s other flagship pens.

The Standard model features a long rubber grip and ABS plastic barrel made with recycled materials. I've been carrying the 0.5mm Coastal colorway in my shirt pocket for the past two months, rotating through approximately 80 pages of notes weekly.

At 10 grams, the Standard sits comfortably in that Goldilocks zone where you don't forget you're holding a pen but your hand doesn't fatigue during extended use. The rubber grip extends further up the barrel than typical gel pens, which I appreciate when my grip migrates during long annotation sessions. The grip texture is subtle enough that it doesn't collect desk grime like some rubberized pens do.

The spring-loaded wire clip gets daily use clipping to my Midori MD notebook, and after two months it still has good tension. These clips open wider than standard pocket clips, making them practical for thicker notebook covers. I've successfully clipped it to a 5mm stack of documents without concern.

Available in both 0.38mm and 0.5mm with eight different calming barrel colors, the Standard works well as a testing ground for the Zento ink system before committing to pricier models. All Zento barrels accept the same refills, so your initial tip size choice isn't permanent.

The Zento Flow model represents the middle tier upgrade. It pairs a softly colored ABS plastic upper barrel with a long anodized aluminum grip section, creating a two-tone design, and weighs 14 grams. I've been using the Jade 0.38mm model for detailed work like annotating technical documents and filling out customs forms.

That 4-gram weight difference from the Standard becomes noticeable during longer writing sessions. The aluminum grip lowers the center of gravity compared to the all-plastic Standard, which some users love and others find too forward-weighted. I fall into the former category. The metal grip section measures just under 11mm in diameter and runs longer than most pens, giving you more real estate to adjust your grip position.

The Flow comes in four mineral-inspired colorways: Fluorite, Agate, Jade, and Hematite, all featuring that distinctive metal grip that matches the barrel color. The metal section does get cool to the touch in winter, which might bother some users. During Tokyo's humid summers, though, the non-slip aluminum proved superior to rubber grips that can get sticky.

One practical consideration: some users have reported the metal barrel being too slippery to hold comfortably. I haven't experienced this personally, but I tend to grip pens firmly. If you prefer a cushioned grip feel, the Standard's rubber section might suit you better despite the Flow's premium appearance.

The Signature model features a matte metallic aluminum and brass body with a magnetic cap, weighing 22 grams. This pen targets a different user entirely than the retractable models. The magnetic cap creates a satisfying click when posted or capped, and the pen balances perfectly when posted with the weight slightly forward.

I received the silver 0.38mm Signature three weeks ago and it's become my desk pen for contract reviews and important correspondence. The weight is designed to be well-balanced when posted, with a lowered center of gravity that allows the pen tip to glide freely across paper. The 22-gram heft provides enough feedback that you always know where the pen is, but it's distributed well enough that fatigue doesn't set in.

The cap-posting system deserves specific mention. The magnetic connection is strong enough that you won't worry about it uncapping in your pocket. I tested this by carrying it loose in my bag for a week, and it never came apart. The cap posts securely on the barrel end with an equally satisfying magnetic snap. When capped, the pen seems short, but posting the cap brings it to the perfect length.

One reviewer noted needing painter's tape on the refill to eliminate slight wiggle when writing, but I haven't experienced this issue with either my unit or the black 0.5mm model I tested it myself. This might be sample variation.

The Signature comes in two configurations only: silver body with 0.38mm or metallic black body with 0.5mm. Both use hard plastic for the grip section rather than rubber, which I prefer for extended writing but might not suit everyone.

The uni-ball One series remains the obvious comparison point. The One uses pigment-based ink designed to sit on paper surfaces for maximum color vibrancy, and it's available in over twenty-five colors in the 0.38mm size. In direct comparison tests, the One had the most saturated ink and felt the smoothest overall, though it wasn't as consistent as the Zento. Some users report the One occasionally skips at the beginning or middle of strokes, which matches my experience. The Zento trades some of that deep black intensity for more consistent flow and reduced friction.

The Jetstream series operates in a different category entirely. Jetstream uses low-viscosity oil-based ink that dries almost instantly and doesn't react to highlighter, making it superior for forms and documents you'll highlight later. But one reviewer noted that the Zento ink is as dark and smooth as other gel inks, performing like a gel on the page. For pure writing comfort over extended sessions, I reach for the Zento over Jetstream because the water-based gel formula requires slightly less pressure.

In a direct test between the 0.5mm One, Signo RT1, and Zento Basic, the One dried quickly with high water resistance, the Signo dried slightly slower but smeared in water, and the Zento dried slowest but showed high water resistance with the finest line. This tracks with my field testing. The Zento takes about 3-4 seconds to dry completely on standard paper, compared to 1-2 seconds for the One.