There Are Pandas, and Then There Are Pandas.
And this isn't either of them! The Pandas we're talking about here, are watches, not bears. And what got me thinking about them (again) was a link posted this morning by @cm.rook who pointed a few of us to the very attractive (and not terribly priced) Yema "Rallygraph" Panda which, in it's most traditional arrangement, looks like the one on the left, but can also be had in the version on the right: The model on the left is a true Panda, while the model on the right is called a reverse Panda. The reason for that distinction is clear--Panda bears, only come in the first arrangement. Now at this point, everyone should be thinking about the most well-know Panda, The Rolex Panda, which is actually a Daytona, and among Rolex Daytonas, the most famous of which is the Paul Newman Daytona, which was famous first, because it was Paul's, and second because it sold at auction for $17.8 million (US Dollars). The story of that auction is well-known so I'll only...
Nov 8, 2019
Main thing to consider is nib size and type. An ECO in EF (extra-fine) is about the same line/width as a Pilot Metropolitan F. However, in my hand, the ECO's EF nib (a German-sourced unit, from JoWo I think) is smoother and a better performer.
For $50, you can consider upgrading to a TWSBI 580. It's the "upgrade" version of the ECO, thought the ECO came later than the 5xx series. The 580 adds a swapable nib unit, metal fittings, and a faceted barrel for visual appeal/reduced rolling. It's not postable like the ECO is, so that may be a consideration.
At $70 is the VAC 700R series, which is the "ultimate" pen in their catalog. This features a VAC fill system, and even has a dedicated inkwell for use with it. However, I would avoid the 700R until you are more comfortable with filling systems as it's a bit more fiddly (you need to "unlock" the pen every time you use it more than a page or two).