Oh! Those works too?!? I know them! They blue and much harder than the pencil erasers. I'm going to the stationary stores now!
Those are the ones I use, yes, blue ones.. And quite useless for the intended purpose - it would make a hole in the sheet, which WOULD indeed remove the pen writing, but not really the way we wanted it to

. That is why I have a bunch of new or little used ones from AGES ago.
It does remove also the "shine" on the part - but I think ALL methods must. It's not fast either, but it does work, and it's not hard to get...