This is my second or third set of these pens. I LOVE them.  I'm a leftie, so I need to write with something that dries quickly and these fit the bill.  Now, they will go through a standard-weight notebook page (not onto the next page, but you can't use the back), but they don't bleed through on 20 lb paper, which is what I primarily use them on.  There are only a couple of colors that are too light to show up in my planner, so I really do get a lot of use from this set.