I got one of the grifos pens as well, the pen and the city from a drop here a number of months ago. I was having g problems with the ink flow initially. I was trying to use their cartridges that came with the pen. They did now flow at all and made for an unpleasant experience.
That said, once I switched to a converter cartridge, it flowed wonderfully and became a joy to use. Just a heads up to whoever purchases this pen in case it doesn't want to write well out of the box.