The Rotring Rapidograph uses a cartridge, and there is technical language, which I won't attempt to repeat, that says in essence--little to no maintenaince.
The cartridge is easy to install, once you read the instructions (I didn't, lol). The pen feels good in the hand, but, so what? you ask. How well does it work?
I chose a .18 size nib, which is small, and the size I would use most often. After about two weeks, the line is as crisp and fresh as it was brand new, even after heavy use on textured paper. Which is what I would expect from a good technical pen. I draw constantly, and the Micron Pigma's nibs, of similar size--.005 and .003--would be wearing down within that time frame.
Pros: The Rotring rapidograph performs well and requires little maintenance.
Before I get to the Cons--most technical pens have little tubes that you can refill with bottled ink. That's good, because the bottled ink is cheaper, and easy to find, and you can switch colors, and sometimes the type of ink.
Except--there is a saying. You can't spell LAME without ME. Yup. I carefully squeeze that ink into the little tube. And watch it splatter across the wall, the floor, me, and generally go everywhere except into the little tube. Plus, I'm impatient. Most technical pen tips, especially smaller nib sizes, will clog up. Then you take them apart, and if you don't bend them (I do) you soak them in water, alcohol or special cleaning fluid. Sometimes for days. Which means you can't always use the pen when you want it.
So, I need a cartridge-based pen. Okay. I want a cartridge based pen.
Cons: The pen isn't cheap. Prices vary by nib size. At DickBlick's the Koh-i-noor Rapidograph .18 mm is $21. 99, where the Rotring Rapidograph .18mm is $35.51.
You have to find and buy replacement cartridges, which run around $7 plus shipping and handling for 3 cartridges.
Both the pen and cartridges are hard to find. DickBlick's, NYCentral Art Supply and MisterArt all carry them, but I haven't found them at other online art stores that I'm familiar with. I have not been able to find them in any of the three art stores in the Portland, Oregon area.
I can't say that the performance is better than the Koh-i-noor technical pen. On the other hand, my Koh-i-noors all lie unused due to bent nibs and the desire to avoid ink clean ups. In the recent past, I've been using Micron Pigmas and truthfully, I could buy a lot of Microns for the cost of this pen. But I'm tracking how long the cartridge lasts, because it might be cheaper in the long, long, long run.
If you go looking for the Rotring Rapidograph, be aware that the Rotring Artpen is an entirely different animal. It's far easier to find, but is more like a fountain pen. There are also older versions of the Rotring Rapidograph that don't use the cartridge, so be careful to get what you really want, if you buy from ebay or other auction site.
Meanwhile, I'm really enjoying using the pen. Here are some of the drawings I've done so far, using it for the fine detail and shading.