The problem with the SlimLine pencil is the SlimLine pencil. It's a POS.
I made 30 of them as Christmas gifts in an engineering office where I worked. The average time between opening the box and not working was less than a week, and there were a couple that didn't last out the 1st day.
The only way to get a good "click" mechanism is to buy a "Pentel" pencil, tear it apart, and replace the plastic barrel with one we have made. Besides function and durability, they are available in 0.5mmm, 0.7mm, and 0.9mm leads.
The Peffect Fit Convertible makes a good pen and pencil set, I haven't had problems with pencil failures, and the pen and pencil look like they belong together in a set.
This is my personal experience with the pencil kits. Others may have a different experience.