The nib was 'destroyed' by the second coat of the sidings and points in the photos - about 10 feet of track and three points.
Luckily, they ship the pen with a spare, so I should be able to use it until it's empty.
The nib is a little large for the frogs, etc, but you can get decent coverage, and I plan to cover up any gaps with grime from the airbrush.
In it's favour it's clean, simple, you get very good coverage with a few coats, and no overspill, and it's very very quick to use. overall, I'd recommend them.