Here are some Filofax brand pens, old and new. It's interesting that the two older pens (pictured in the center) are slimmer, just like the pen loops in older binders. The two newer pens are both shorter and thicker, probably so they can fit in mini size binders without protruding over the top. All of these pens arrived in pre-owned organizers that I purchased.
The Filofax keychain on the right was gifted when I purchased new old stock binders from Bouteia. It's heavy, opens on a hinge and closes with a magnet, and can hold pictures inside much like a locket.
These next pens are ones that I purchased directly from "mom and pop" stationery and pen stores. I was able to touch and actually write with them before deciding what to buy. They may cost a bit more than online shopping, but the exemplary customer service is priceless. If you ever get a chance, visit Warwick's in La Jolla CA and Penchetta Pens in Scottsdale AZ.
From top to bottom: Lamy Safari Rollerball; Penchetta Stone Rollerball; Parker Urban 5th Technology; Parker Urban Rollerball.