The release of the TWSBI ECO can fairly be described as a pen world sensation. We needed an affordable, piston-fill demonstrator, and the wizards at TWSBI made it happen. And they did it without sacrificing many of the features we've come to love on their more expensive models.
In fact, the only difference I can find between the ECO and the Diamond 580--that relates directly to the function of the pen and not to personal taste or aesthetics--is that the ECO nibs can't be as easily swapped. They still can be, but they lack the screw-in nib and feed unit of the 580. It's a feature that clearly takes more time and effort to manufacture, so it's understandable that it would need to be dropped from the ECO model.
There are a few other things that I don't like about the ECO, but they're more matters of personal taste. I find the smooth plastic section to be too slippery, and the odd triangular barbs at the end of the section that seem to be there to stop your fingers from sliding forward just end up jabbing me, instead. If there was a flared shape all the way around the section, it might work better for me. Those barbs, though, are a real pain in the callus. I grip my pen close to the nib, and this pen wants to punish me for it. It's not as much of a problem for making quick notes, but I do start to notice it during longer writing sessions--and everything else about this pen seems designed for longer writing sessions. But if there's one thing that takes a pen off the "great for long writing sessions" list, it's a bad section.
Another issue that can be a deal-breaker for some is that it doesn't post well. It's wobbly, unwieldly, and I sense a distinct risk of accidentally turning the piston knob. But at least the faceted cap won't roll around on the desk.
There's a lot that I love about this pen, too. I like the look of it. It's made almost entirely of clear plastic, so you can see all its guts, plus your lovely HUGE pool of ink sloshing around inside. The piston knob and cap are made of the prettiest, limeiest, greeniest plastic that stole my heart the minute TWSBI revealed it. I wasn't going to get an ECO, originally--I figured since I had a 580, there wasn't much point. The Lime Green changed my plans.
The #5 steel nib is a little dreamboat. I have pens that cost four times this much that don't write as well. The extra-fine is not as fine as a Japanese EF, but it's finer than the European EFs that I've tried. The medium is also a shade finer than my western mediums. Both have a little feedback, but aren't scratchy. They're nicely wet, especially the medium, and even the EF shows some shading in the ink I'm using (Robert Oster Signature Summer Storm--it's a good thing I love this ink, since I have two TWSBI tanks full of it, now!). All the inks I've tried have flowed well.
The clear section gives a neat view of the ink running through the feed. It made me a little nervous at first to see ink pooling right under the plastic, but I've had no trouble with leaking at all. The nib and feed seem well-fitted enough to keep the ink from escaping.
If you do need to do any maintenance on your pen, the nifty box also contains a wrench and some silicone grease, which you can use to seal threads or lubricate the piston. If you do decide to take your pen apart, I recommend watching some YouTube videos to learn how. The paper instructions are helpful, but aren't much of a substitute for a demonstration.
Overall I would say this is an excellent everyday pen, and it plants itself firmly at the top of my list of pens I'd recommend for beginners. This is the pen I wanted when I was in college, fumbling with cartridges in the lecture hall. I hope they keep making fun new colors, and I'm looking forward to seeing what TWSBI's next game-changer pen will be.
(JetPens provided this product at no charge to The Pen Addict for review purposes.)