I’ve written a few times about how I like the Fisher refill, and while other pens hold this cartridge, some very versatile pens, I usually ended up back with the AG7(affiliate link) or the Shuttle (bottom). It’s hard to find a ballpoint made as nicely as these.
Both are fundamentally brass pens. A push-button design with a side button release. Both unscrew into two halves to replace the cartridge, and both have retained springs and no loose parts when disassembled.
So it might seem that they are interchangeable, but they aren’t.
The Shuttle (bottom) has a narrower body, but a profile that makes the grip thicker in the writing position. The AG7 has a thicker body, but it narrows further from the point, so it’s a more slender pen to write with. The AG7 is also heavier and more expensive, and has a clip that has more capacity than the Shuttle. It also has less reveal, which can make the pen difficult to remove from pen sleeves. I had a clip break on an AG7 from fatigue. It was about 9 years old and was my daily pen for most of those years. Fisher replaced the pen free of charge, no hassles.
The Shuttle’s clip has a tighter grip, but it’s not a design that will recover from being pushed very far – like over the hem of some jacket pockets. It’s a better clip for a shirt pocket though, where the AG7’s clip sometimes doesn’t grab very well.
The mechanism on both is very solid, and both pens feel good in the hand.
The Shuttle is available in several finishes, and the G4 Gold Grid(affiliate link) is the one I prefer. I bought a CH4 chrome one thinking it would be similar to the AG7, but the spiral knurl isn’t sharp like on the AG7, it’s dull and pretty much useless. The CH4 is also profiled more like the AG7 in the grip area, instead of being thicker. The AG7 is available only in the spiral groove grip, but it’s quite sharp and provides a firm grip.
I use them both, but the AG7 continues to the one I favor, even though I think the CH4 is a bit more comfy.
Most ballpoint pens are pretty darned reliable. The Fisher cartridge adds the ability to write at angles, and I think they are exceptionally smooth when used often. When used infrequently they tend to gum up a bit faster than regular ballpoints. While the cartidge will fit anything that takes the universal Parker refill, these solid body pens have a nice mechanism, feel sturdy, and absorb real world treatment without complaint.