TWSBI Mini Review…Finally

TWSBI 540 and Mini

I’ve had the TWSBI Mini ($50-$55) since Christmas but I haven’t reviewed it because I’ve been waiting for a new EF nib unit. Initially, I got it with the F nib thinking I’d like to be able to compare the F nib with the EF nib I have on my TWSBI Diamond 540*. What I discovered is the F nib is quite broad and made me quite sad — I tend to prefer either razor fine or italic/stub nibs, no in-between. So, in order to give a fair and balanced review of the new Mini, I decided to wait until I could swap out the nib unit with the EF and compare apples to apples.


I liked the overall looks of the clear demonstrator model of the TWSBI 540 so I purchased the clear demonstrator Mini as well. The clip shape is ever so slightly different (I think the new 580 uses the same clip design) and TWSBI added threads to the end of the pen so that the cap will post snugly. The silver band at the base of the cap is narrower as well. Otherwise, the size is the only visible difference between the 540 and the Mini.

Size comparison

The 540 is about an inch longer than the Mini which measures about 4.5″ capped which is about half an inch longer than a Kaweco Sport. The barrels on the 540 and the Mini are the same diameter. Uncapped, the Mini is about 4.25″ long and with the cap posted its 5.5″ long which is comparable to most full-sized pens. The Mini weighs 20gms (full of ink and capped) which is 7gms heavier than a Kaweco sport but 8gms lighter than the full-sized 540. In my current pen collection, the TWSBI 540 is as weighty as my Lamy Studio which has an all-metal body.

Fountain Pen Weights

TWSBI Mini nib

The nib of the Mini is more slender than the 540 nib but the same length with the sample decorative filigree and logo.

TWSBI mini review

As expected, in writing tests, the Mini performed exactly the same as the full-sized 540 but was more comfortable in my hands for long writing sessions. The nib is smooth on the paper and writes continuously without any need to prime it. (If pausing while writing, some other fountain pens will dry out requiring that I scratch on a scrap of paper to get it going again which is often referred to as “priming.”)

The ink capacity is not as large as the 540 but both use the same built-in piston filler which is easy to use. The Mini has held enough ink to keep me writing for about a week without needing to refill so it definitely hold more ink than the standard European cartridge.

TWSBI mini writing close-up

If you are looking for an upgrade to the Kaweco-sized pens or want to use a lot of bottled inks, I recommend the Mini.

*The TWSBI 540 has been discontinued and replaced by the upgraded Diamond 580.

(This pen was tested on the Miquelrius medium flexible 300 grid paper book purchased from B+N.)

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  1. Thanks for the great review. I would love to get a Mini: I’ve been waiting for them to release a solid colour pen. I’m only worried about all the cracking issues I’ve read about. Have you had any issues with your 540?

    1. No. I’ve had no issues with the 540 or the Mini cracking though I am not overly forceful when twisting the cap back on or filling the reservoir. I suspect overtightening is what has caused the cracking. Also, I do not leave my pens in the car or other places where it might have to endure extreme temperature changes. I am also hoping that TWSBI offers some solid color bodies but the nice thing with the clear is that I can always see how much ink I have left and whether I’ll have enough to last through the day or if I need to refill. Best of luck to you!

  2. God help me, I’ve just bought one. Been thinking about it since before Christmas, but this review was the straw that broke the camel’s back…

      1. The pen arrived a couple of days ago: definitely worth sacrificing the camel. I went with the ‘Classic’ design and a medium nib which I think is on the fine side of medium… funny, considering your disappointment with the actual fine. Writes beautifully though.

  3. I finally got a mini after debating over it for a while. It was fine out of the box, nothing spectacular but pretty nice. Unfortunately only a couple of weeks later I already have two cracks. I’ve only filled it once and have yet to take it apart so its definitely not from over tightening or mishandling. Its unfortunate they still haven’t fixed these issues, I love demonstrators and TWSBI makes the only affordable piston filling ones 🙁

  4. Can you name five “razor fine” Pens/nibs that you like? Is this one of them? I am always looking for a good “razor fine” nib.

  5. Can you recommend five or so “razor fine” nibs/pens? I am always looking for a good razor fine nib. Is the TWSBI one of them?

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