Safrut is not “vacuum-sealed” and it was influenced by the calligraphy of the gentiles. Until 700 BCE, reeds were the most common writing instrument and that explains why the original Halacha is that Hebrew scribes must write a Sefer Torah with reeds. After 700 BCE, feather quills were "discovered" and became increasingly popular for writing purposes (source). In fact, some of the Dead Sea Scrolls, which are dated around 150 BCE were written with feather quills rather than reeds (source). That explains why the Ashkenazi scribes stopped using reeds, rather favoring the popular and "new" feather quills. I've also heard that the reeds in Europe were not as good and sturdy as the reeds found in the Middle East, and if true, this is another piece of this puzzle.
The main pro of using feathers is the fact that it stays sharp for longer than a reed – at least twice as long. Reeds are wood-pencils and wood wears out very quickly, forcing a scribe to constantly cut it sharp (it’s critical for a Sofer to have a sharp Kulmus, otherwise the Taguim will not come out properly).
The Sefardim however kept the original tradition of reed kulmusim by and large and until this day Safrut stores sell reeds alongside with feathers in their shelves. Because of the sharpening issues the Sefardic scribes usually don’t do the Taguim themselves, they will rather finish the Parsha and hand it over to a Metaieg, a Sofer who specializes in writing the Taguim.
The Poskim have subscribed to the feather quills and will allow the Sofer to use any instrument to write, even though it’s clear that the original Kulmus was from reeds.
In fact, a few other alternatives have appeared now that we are living in a technology-intensive world:
- Plastic kulmus, which is sold already sharpened, that is available for cheap and it’s quite good. I’ve used it in my first Meguila.
- Steel kulmus, which is pretty much a fountain pen made in the shape of a feather quill. I’ve tested it but it didn’t work well for me. And it’s expensive.
- Gold-dipped feather Kulmus. This is one really expensive, but you can write a whole Sefer Torah without having to sharpen your quill.
Aside from the obvious advantage of not needing any sharpening, the plastic/steel/gold kulmus hve another great pro. When writing with a feather, you will have to always cut it in the same size, in order to ensure that all the lines are written uniformly. But in practice that’s very hard to accomplish and, unless you are a master scribe, the letters will come out different in every column - sometimes thinner, sometimes a little thicker and that's not aesthetically good. With a plastic/steel/gold kulmus all the letters will be the same, effortlessly, since you don’t have to sharpen it.
So next time you see a Sofer writing with a (special) fountain pen, don’t shoot him. It’s permissible to write with other instruments besides feather quills.