Office equipment / supply places have better refils than what come with some the pens. A few people have had problems selling a pen for $25 + and then having the customer complain about the original refill not writing well. It might have been a bad factory run batch or something. There was a discussion on this about a year ago. I don't know if the situation has improved or not. I haven't had a problem with most, but then again I haven't turned a lot. I did have a problem with a couple of pens that had that problem with the original refill - these were slimline pens purchased from a couple of different places.
I personaly like the refills that come with the kits better than the cross brand refills. I have had more problems with the actual cross brand than the others.
Just my .02 worth.
I have also been looking at the space pen refills.
I second what Ryan said. It happened to me several times that a customer called me up and asked if they can buy refills from me - the original brandnames (either one) they bought were not as good, i.e. smooth writing. I have myself made the same experience, too.