The TWSBI story is a reasonably well known one among fountain pen afficionados (I don't account myself one of those, although I have a users interest in them) and is an interesting study in the use of modern communication to develop and market a product. The pen pictured above was developed with a huge amount of input by members of the Fountain Pen Forum, as TWSBI's next product, the V700 pen will be.
The Diamond 530 also fits into the idea of the "Self Repair" manifesto I posted in December - it's designed from the ground up to be user serviceable and adjustable, even shipping with the tools you need to dismantle and re-assemble it!
The TWSBI Diamond 530 is generally well regarded, and TWSBI themselves are also, largely because of their responsiveness to consumers. The linked article focusses on the company's origins, and the development of the Diamond 530, with a link to a more comprehensive review of the pen.