Ultra-lean saddles look extreme but should provide more comfort than bigger ones due to supporting you in the areas you need it. The broadest section should support the rider’s sit bones, but it’s worth noting that men’s sit bones are closer together than women’s.
The cut-out or drainage channel will naturally aid ventilation and drying of your shorts. It’ll also take the pressure off your perineum. The channel can be a reduction in the pad’s thickness or something as extreme as a hole, as seen in ISM’s designs.
Triathletes, especially long-distance ones, will spend extended periods of time on the aerobars. So a tri-friendly saddle should have a narrow, flat profile due to the rider being in this aggressive forward position, with their weight placed towards the nose.
The saddle railings tend to be made of steel, aluminium, titanium or carbon, with the latter two being more compliant and comfortable, while shaving weight yet adding pounds (Sterling) to the price. You can clip lights, saddle bags or hydration systems to them.
There are plenty of hydration systems that can mount on the rails of the saddle, but tri-specific saddles can also have integrated bottle mounts on the rear with bosses to secure your own bike bottle cage (the Fabric here also doubles as a transition hook).