I find these pens ideal for margin notes in my Bible, They do not bleed through, although they can sometimes be seen from the other side of the page. This in no way reflects on the quality of the ink used in the pens, more of a reflection on how thin the papers is.
By writing lightly the amount of ink used is cut down a little enabling me to write extremely small (wide margins never seem to be wide enough for me)
The colours do not seem to fade over time, - I have used them for over two years now and I would never use anything else for margin notes. They are bright enough to use to underline words or verses without having to resort to highlighters which I find tend to bleed through or fade after time.