A fine pen can be a great conversation piece. But, it is still a writing instrument, and as such, should write well. Take a fine-looking automobile, sure it looks nice, but how does it drive? A car is only as good as the tires that it rolls upon. And a pen is functionally only as good as its tip. So, what do you look for in a rollerball refill? What sets one cartridge apart from another? What makes a Schmidt rollerball refill different from a Hauser rollerball refill?
There are a number of types of pens. The humble ballpoint pen is clearly the most ubiquitous. And while fountain pens offer a great writing experience and classic look, they aren't for every situation. Enter the rollerball pen. The rollerball pen was introduced as a way to capture that effortless writing experience that you feel when using a fountain pen, but with the convenience of a more easy-to-use tip and refilling cartridge.
Rollerball pens typically use a water-based ink similar to that found in fountain pens. The main difference is that the ink and tip on a rollerball are packaged into a cartridge. This eliminates one of the traditional problems with fountain pens - refilling. Of course, fountain pens now have cartridges as well, eliminating the problem of refilling.
A rollerball pen doesn't require significant pressure to make it work. A very light touch is all that is required. Unlike a ballpoint, where the ink is a gel and requires more pressure to make it work. A fine rollerball simply glides across the page.
Rollerball pens are also a bit more durable than fountain pens, in the sense that you can lend a rollerball pen to a friend. Lending a fountain pen to someone else can lead to problems, especially if they have never used one before! Fountain pen nibs also get 'used' to their owner, that is, they have a memory. And if not careful, a friend could break your fountain pen nib!
Rollerball pens do not have this issue, making them ideal in a corporate setting. They travel well, even on airplanes. They are easy to use, since they only need a cartridge.
Most rollerball pens have a cap that covers the tip of the pen. This is to help prevent the ink from drying out (although there are rollerball refills designed specifically for capless pens). Since the ink is typically water-based, the ink dries on the paper, essentially as the water evaporates. One point to consider is that since the ink flows better than a ballpoint pen, the experience is a little 'wetter'. If this is a concern, look for a refill that uses a gel-based ink. These inks are a bit closer to a ballpoint pen experience, and have the side advantage of having the ink in the cartridge not dry out as quickly.
Although the tips may look similar, a rollerball refill is functionally different from a ballpoint refill. From a slight distance, they look similar, but the cartridge shapes are not the same, and as such they can not be interchanged. The tip of the pen is very important and you will typically find a ceramic tip in a rollerball (again, think smooth) versus a steel ball in a ballpoint. This is important for a great writing experience.