I’m a TWSBI user, the 580 is my main writer now, simply because it holds so much ink, and it’s fun to watch the ink bubble slosh around inside the barrel.
The other nice feature of the TWSBI is I can unscrew the nib off the pen and fill the pen barrel directly with a straw. I use an ink syringe with a blunt tip to fill up my pen. Its much less messy to refill, and also to clean out the pen when I want to switch out colors or regular pen maintenance.