Obviously the amazing reviews for these pens were written soon after the first use. I bought a box of red pens. It is true that the stroke is formidable, but the tip dries within a few hours of use (often earlier). They can be unblocked by putting the refill in hot water. However, they still last a couple of hours after this treatment before they get blocked again. When this happens, I take a new pen (with the sealed tip) from the box to continue my work and I observe the same behaviours in these new pens. Now I have four on the go (I put them in hot water all at once). I will never be able to use them completely as this is not sustainable. Too bad, because they write really well until they don't.