The line width that this pen lays down is smaller than most of my other German EF nibs. It's closer to a Japanese F, which is fine in my book. The line is also very crisp and well-defined. There's no burping or feed problems when writing, and the ink flow is very consistent without being dry.
The nib writes well from the start with no stuttering or skipping. Even after being uncapped for a while, it only takes a couple of light strokes to get the ink flowing again.
The steel nib is very rigid, which means there's no flex to speak of. If that's what you're looking for, you'll have to look somewhere else as TWSBI nibs are known to be very stiff. It's a reliable, good writer, and that's what matters!
Overall, the TWSBI Mini AL in Blue is a solid iteration on an already great pen. The added aluminum parts not only increase the quality of the pen, but the aesthetic as well. It costs a bit more than the regular Mini, but it's well worth it. The blue edition will likely sell out soon, but there's always the standard silver AL! For most other piston-filler pens, you're looking at spending well over $100, so the price point (sub-$70 range) of the TWSBI Mini is unbeatable, especially considering the quality you can expect from them.
(JetPens provided this product at no charge to The Pen Addict for review purposes.)