For its price, it is one of the best purchases and is highly recommended. It goes without saying that, apart from Pentel refills, you can also use ones from other brands if you want a thicker tip or better color or writing feel. Its weight is relatively comfortable, and I mention this because for extended writing, the protective cap should be completely removed from the pen for better balance in the hand.

Saturday 27/11/21 Purchase
Impressive sturdy construction and minimalist design at first contact.
3-4 pages later with drawings and texts, the impressions are excellent: Very good writing with minimal pressure, and well-balanced in the hand. Theoretically, with a thickness of 8 millimeters, it will suit any hand size, and it is the perfect size to always have with you: No need to search for it for an hour in bags and pockets, nor is it bulky like a marker!
The quality and finish are at excellent levels for the purchase cost, and its replacement is affordable at €1.30.
The ink does not leave smudges on prolonged lines in hasty or continuous writing so far, but I reserve judgment on this because it is still new.
Over time and in its finishes, it will show if it remains waterproof.
I was impressed by the ink that dries immediately. When we say immediately, I mean literally! Even if you intentionally try, it does not smudge the paper!
The ink's duration is still being measured, as well as the finish.
A relevant update will follow.

23/12/2021 UPDATE:
Today the ink stock just ran out *...
The (additional) pros:
- Comfortable writing on almost any surface. It literally writes almost everywhere: From glossy paper to... plastic bag! And it even dried relatively quickly on plastic!!!
- The flow, even with hasty lines or fast writing, is continuous and uninterrupted. There is no need to repeat a line or letter.
- It wrote until the last line like the first day, without running or "drying out" the ink.
The (only) con:
Like most GEL-type pens, it does not have a long lifespan... It didn't even last a month...
* Replaced with the same brand's blue pen, and there will be an evaluation for that too.

Happy holidays with good health to the whole world!