This post uses an air shock for suspension duties instead of the more common elastomer, and this has two main advantages. It's slightly lighter, but more importantly you can easily tune the suspension action to your weight and the type of riding you'll be doing.
There's a Schraeder valve at the base of the post for you to add and remove air to make the action softer or firmer. You should ideally use a shock pump for this, but in practice I found that any small-volume mini pump could handle the job. A solid double bolt clamp holds the seat in place. At 340g you're sacrificing about 100g over a standard post to get your 40mm of suspension travel, so is it worth it? There'll no doubt be dissenting voices complaining about the loss of efficiency due to the changing pedal-to-saddle height, but you can pump up the post so that it only compresses on larger impacts, which will save your bum without sacrificing power. It definitely improves comfort on a longer ride, such as an Audax or a long TT. Mainly, though, this is a post for commuting, Sunday riding and general knocking about. Run it soft and it takes the jarring bumps out of a ride with minimum fuss.