Looks like between Chomas Creations (Custom Crops and/or Staples pens) and Cri-Kits we have the gel pen holder conquered. Both holders and the pens that accompany them will do a fine job on small images cut directly from a cartridge as shown in the image below, drawn at 3/4 inches high.
There remains a significant problem when cutting from a computer however. I compared a Provocraft cartridge image with a similar, node optimized, SVG in SCAL and MTC. As you can see, all of the computer-driven versions have significant “jiggle” compared to the direct cartridge image. (Click on the picture to see the enlarged image, also drawn at 3/4 inches high.)
The Chomas holder with Staples pens seems to do a slightly better job with the computer-driven drawing than the Cri-Kits pen/holder (at least with the dark blue pens I tested) but the results at small sizes are still not very impressive with either. (For reference, the top upper case ABC is 1/4 inch tall)
It helps some to increase the size of your images. Here is the same node-optimized letter at about 1-1/2 inches high using 3 different pens. As you can see, the ballpoint Silhouette Sketch pens do not show the jiggling quite as much. It makes sense that the more free-flowing the ink, the more pronounced the jiggle is.
I also tested various speeds and pressures but could not see any improvement. I also tried optimized images (minimum nodes/control points) and polyline images (many nodes/control points) and the results were still unimpressive. My guess is that the disparity has to do with the coordinate systems for cartridge cutting (perfectly matched) versus computer-driven cutting (imperfect conversion). I am further convinced that this is a machine limitation because I’m told that the same files draw smoothly with a Silhouette cutter, and because no one else has been able to show me an SVG that cuts as smooth on a Cricut as a cartridge.
I also tested the Staples ink tube/tip in the Cri-Kits pen shell and vice-versa. You can enjoy using the inexpensive Staples pen innards as refills in your Cri-Kit holder, just turn up the pressure until you have contact with the paper. Unfortunately, the Cri-Kits ink tubes do not work in the Staples pen barrel, because the exposed tip is too long, even at minimum pressure.
BTW, there are lots of great gel pen ideas hitting the blogs right now like this post from my good friend PapaSue , this one from Denise at PaperPastime, this one from Shelly at Paper Flowers and this one from Samantha the Scrapmaster.