I purchased this pen to use with metal plant markers, also from you. It made a clean dark line that is easy to read. It has been out in the rain and looks as good as new.
So far this pen is a success. It worked easily on markers balanced on one hand, and so far has stayed on through some serious rains. We'll see about 120 inches of snow melting around it - the real test.
This is my first year to use this pen and it has worked very well for me. Good dark color to mark my markers so they are after a summer still very clear to read, which is what I wanted from this pen.
Every other "permanent" marker fades after a season or two; these are readable years later, and the fine point makes them easy to use, too.
I have used many other brands but this pen held up the longest for marking rooted cuttings. The point is particularly durable and it even marks when the tag is damp.