I reached for my smoke colored TWSBI Vac 700 today and started to uncap it -- and only part of the cap came off.
This is the second Vac 700 of mine that's had a major component snap in two. I didn't abuse it. There was no warning. It just came apart.
I went through the cracking problems with the Diamond 530. I assumed TWSBI had figured it all out and fixed things on the Vac 700. They had years to straighten out their difficulties, and the Vac 700 was their new flagship pen, and I hadn't heard about anyone else having problems with them. And besides, I simply adored EVERYTHING else about these pens. After the first one failed, I was willing to shrug and chalk it up as a freak occurrence that probably would never happen again. But no more.
The only thing I can figure out is that TWSBI are injection-molding these pens out of styrene, or some sort of thermoplastic that simply isn't durable enough for the job and is never going to be. That's how they can make their pens so cheap, but no amount of jiggering the design is ever going to turn this into a durable material. This is why other pens companies machine theirs from rods of cast acrylic plastic, or similar materials.
I've been recommending these pens to everyone, and now I am ashamed. Obviously I won't be doing that anymore, and I won't be carrying and using them anymore.