I use an old A5 Filofax, I’ve had it for 30 odd years, not with the original diary I might add. Filofax paper is a bit poor and finding a decent pen to use is, well, you have pens you like but the paper ruins the writing experience.
Above we have from top to bottom, a gel pen, a Parker fountain pen, sharpie and a Parker roller with Mont Blanc refill.
The gel pen smears on to the other leaf if you haven’t allowed enough drying time, the Quink ink in the fountain pen bleeds but the sharpie and the roller ball give a nice clean write.
I have to say that the best note taking paper for the fountain pen is a Staples M.Arc pad.
The paper has a very fine smooth surface, I think it may have china clay in it. It give a firm smooth write so you can write quickly with an inkpen with no bleed.