My wife got me this Hongdian 1851 for Christmas last year, along with the astronaut pen holder. Since I keep it out on my desk, it is the pen that I reach for most often. It has the finest line of all of my pens and I keep it inked up with iroshizuku murasaki-shikibu, which is an incredibly close match to the body of the pen. It has a lot of feedback without being scratchy, and is great to write with.
The calculator is a Casio fx-260 Solar II, which Kristi also got me for Christmas some years ago. It's the calculator that I grab most often since it is the easiest to get to. It's my little Apocalypse Calculator since it has no battery and is solar powered only.
I have two 1851s and they are the narrowest sections of any pen I own. 7.9 mm at the thinnest, but it has a pronounced bump at the end of it to keep your fingers from slipping into the nib and feed. They are comfortable enough for me to write with, even if I do prefer a wider section. For a pen that costs less than $20 USD, they write great, feel substantial, and come with a pretty good converter. Just be aware that the powder coating wears off pretty quickly with use. The other one that I have is the Forest Rainbow, which is anodized and shows no sign of wear.
I was also impressed with my hongdian (different model).
Much better than Jinhao.
Which other model do you have? I have a 525 EF that was nothing but trouble and had to be benched.
The M2 I posted recently.
That's right! Sorry for the brain fart!