TWSBI is a brand that has a fantastic reputation in the pen community, and with good reason. For starters, most of their pens are priced in what I would consider the "midrange" at around $50-70, but what sets them apart is the quality you get from such an economical pen.
I've been sitting on this 540 for quite awhile waiting to review it, but that isn't because I haven't enjoyed it. I knew specifically that I wanted to buy one in the discontinued Amber finish (which is more of an orange?...) and happened upon this one through Amazon for $39. Steal.
It originally came with a Broad nib which didn't really suit me that well, but Tim from The Writing Arsenal and I were conversing and he happened to have an extra F nib (that he wasn't terribly fond of) so we made a swap.
Of course, the writing quality of the TWSBI nib is superb. I've had nothing but positive experiences with the brand and I feel like I can trust buying new products of theirs when they come out because of it.
The 540 is the predecessor to the current 580 line. Some slight changes made to the 580 include a metal ring that goes between the grip section and the barrel. This was added due to instances of the grip section cracking because people were screwing them on (maybe a bit too tightly?) so TWSBI made the metal ring as a safeguard.
The 540 is a full size pen coming in close to 6 inches in length. Not overly weighty at all due to the all plastic barrel, but with the reservoir fully inked up it feels well balanced. There are quite a few moving parts to the 540 as it is a piston filler which could be a little unnerving for a fountain pen newbie. The build quality of the TWSBIs are good, but I wouldn't say the material is something you're going to rave about like a silky smooth acrylic.
The cap is weighty as it does contain some metal parts and does post, but just slightly. If you are familiar with how the TWSBI Mini cap posts and threads on to the back of the pen, this is not the case with the 540. The barrel is long enough in my opinion to warrant not needing to post it at all.
What is it that makes TWSBI superior to other brands considering the seemingly low pricepoint? I compare it to my recent review of the Pelikan M205... The Pelikan, although a beautiful pen with a decent retail price tag of $195 is in no way superior to this TWSBI 540 in writing experience. Build quality? Definitely as the Pelikan feels very well put together and solid while the TWSBI has a few creaks here and there, but none that inhibit a lovely experience while using it.
I would wager it has something to do with the ideology of the brand and those that run it. TWSBI is a group of innovators and creators. This is evident in the sheer number of prototypes they post about. Not just "look at the fancy new pen we're going to sell" but, "we think this is really cool; what do you think about it?". They want a good writing experience for the end user because that is their purpose, not just to sell pens. Now, this is all speculation on my part, but it makes sense.
If you are looking for a midrange priced fountain pen I'd highly recommend the TWSBI lineup.