The main advantage of anti-shock poles is that they tend to be less jolting on joints (like elbows and wrists) when used on firm ground or rocky terrain. On softer ground, where the dirt, sand or snow provides natural impact absorption, they can sometimes feel “mushy”, and most people would find the benefits negligible. For this reason (and also to prevent lockup due to freezing), you’ll notice that snowshoeing and skiing poles usually do not have the option for shock absorption. Much of the perceived effectiveness of anti-shock poles will depend on the conditions and environment they are used, as well as the user’s personal preference.
As far as weight and reliability, the performance will vary depending on the mechanism (which is usually a spring of some kind). For example, some telescoping poles with a latching lock have anti-shock built into the handle (such as Black Diamond), which keeps the mechanism more protected, but can add weight to the pole. Other poles (such as Komperdell or Leki) have the anti-shock mechanism built into the lower section of the pole, integrated into the twist-lock mechanism. This can result in weight savings, but tends to be less reliable, as it is more delicate and prone to damage. In general, considering there more moving parts on pole with anti-shock features, there is more chance of failure (even if only nominally).