I've tried a couple of pens with Rubio Monocoat - a couple of thoughts...
Rubio Monocoat 2C should be used in two parts - part B is an 'accelerator' but also provides additional durability to the finish, such as a harder finish with more water repellence . However, with the small bottles of part A (20ml) they don't sell the accelerator in an equally small bottle, the smallest being 100ml I believe.
The minute amount required to finish a pen means it is not practical to combine the two parts. We aren't finishing a few square meters at a time, so we are stuck with just using part A as is.
Rubio also suggest that you should do routine maintenance (with a different product). Now its not particularly practical to do routine maintenance on a pen, even less so if that pen is no longer in your possession.
This all said, I like the finish, ease of application and it looks good. It is not super glossy like a CA finish, but more similar to the melamine lacquer. It retains the 'woody feel' that melamine does, unlike CA.
Overall, I will keep trying it and I am curious to see how long the finish will last without maintenance and the part B.
(New to the forum so no idea how to add photos!)